For a blog, you probably don't really need crazy resolution; almost everything is going to have to be re-sized down to around 1Mpix anyway,
Then, pictures should be for illustration; it's the story that 'matters'.. if you have a strong story, people will barely more than glance a pictures anyway, they are not going to be pixel peeping and critiquing your choice of f-top!
My own experience in this arena has bee creating/maintaining my hobby-home pages, for petrol-head stuff, mostly to do with motorbikes and Land-Rovers; some of the most challenging articles as far as photo's go, have been "Photo-How-To" features explaining how to rebuild a motorbike engine, or recondition a Land-Rover wheel-hub; here illustrations are intrinsic and essential, showing folk where to find a bolt or notch or 'something' to stick a screwdriver into. 'Adventure' reports, from off-road excursions in the Land-Rover's or Motorbike meets or rallys, standards for the photo's are far less crucial; it's still 'The Story' they are illustrating that matter most. My own influence & inspiration, really comes from 70's/80's/90's magazines; These, particularly the older ones were very lean on photo's, and a lot of those they contained were often B&W, and reproduction was never particularly wonderful, either way. The "Interest" to the reader, was always in "The Story".. which remains paramount.
Why do you blog? What's the point? What are you trying to tell the world? What's the 'Story'? - You haven't put a link to your blog in your profile; so without doing some cyber-stalking to hunt it down, I don't know. But that is the start. I started my hobby page, around 15 years ago; there wasn't anywhere near as much on the net, blogs didn't exist, and the few home-pages there were were usually pretty lame, and far too often ego-exercises for the creator, showcasing wonderful web-design and not actually having any real content, or showcasing the icons of their hobby, like a car or a motorbike, or a h-fi or fishing rod, and not actually doing much else, and certainly not offering any-one who might see it anything....
THESE, are the crucial questions... in photography, as well as bogging/web-creation;
1/ WHO do I expect to look at this?
2/ WHY do I expect them to look at this?
3/ WHAT will they find 'interesting'
And when it comes to a blog a web-page a book... its the STORY, that has to take precedence; photo's are just for illustration; wonderful photo's rarely stand on their own....
It's another negative trend of the web, people are loath to 'read'; but add that to the old bug-bears of indulgence pages, showcasing fantastic web-design, or personal possessions; it is inordinately 'easy' especially for the 'author' who knows the subject they are dealing with, who has had the experience to expect photo's to 'speak for themselves',, make perfect sens to them! They knew why they were pointing the camera at something.... alien web-viewer DOESN'T.. that's what you have to explain to them to give the photo any 'meaning' or 'relevance' before you even begin worrying whether its a particularly good photo!
Which is all to beg suggestion; looking at the 'whole'.. is a better camera or a new bit of photo-kit, REALLY going to do much for you? Look at the whole; Who, Why, What? How important REALLY are the photo's? Are better photo's going to make an awful lot of improvement to the 'blog' as a whole? And, still stressing 'The Story'... are better photo's going to do as much as a better or more likely simply better told 'story'?
You made comment that ships is big! Err.. yeah.... how many photo's of entire ships do you need/want?! Are any, let alone 'more' going to add much to a blog? I have an UWA, specs say it has a 120Deg FoV at the wide end.. I'm not entirely sure even with that, I would manage to cram a cruse liner into the frame stood on the quay! I also have a full-round fish-eye, that does have a full 180Deg Fov.. I have to be a bit careful with to avoid getting the brim of my hat and toes of my boots in shot! That would probably cram a cruise liner in the shot from the quay.. provided I didn't mind it looking a little like a banana!
Which starts to suggest some of the niggles with UWA lenses, and the distortions you start to get at UWA FoV, before considering how tricky they are to work with, shrinking so much into the frame, reducing 'impact' and including oft unwanted 'clutter' and big expanses of oft very boring for-ground or sky. They are much more useful for opening up small spaces than they are cramming in big ones... but that doesn't much help your big ship shots.... to which, IF those sort of shot's are important, you are probably looking at a much more moderate lens, to 'flatter' the subject, and concentrate viewer's attention, and likely need a helicopter to get far enough away from it, when at sea so as to isolate it from not very nice wharf-buildings and other shipping!.....
Which begs the suggestion of using cruise liner co's publicity shots IF you need to show a whole ship like that, as they will have almost certainly done it, and done the subject far ore justice than you could.... and back around the loop.. WHO? WHY? WHAT? And THE STORY...what illustration is actually pertinent to and going to 'add' to the story you are telling?
Here a UWA may start to make sense, IN the boat, in those more confined spaces, opening them up, and showing what's going on in them.... but still damned awkward lenses to start to get to grips with, let alone exploit.... and if you have low-light issues? Yeah... with a 100+Deg FoV, you aren't going to be using in-camera flash! Well, you could... but you'll tend to get a rather well 'blown' subject in the middle of the frame, that vignettes out to nothing at the edges! You are into the realms of very well conceived multiple flash setups, or studio lighting, or getting down and dirty ramping the ISO for available light....
And STILL is what you are going to get, going to 'add' to the blog? Is it that important or intrinsic to the story? Does it HAVE to be that 'great'?
And you are currently using a compact and an i-phone, because they are convenient; they are 'on hand' where and when shots present themselves... stepping up to a more refined bit of kit, that is that much bulkier, cumbersome, and begs much less 'grab and snap' and a lot more setting up, and 'faff'... are you going to loose more than you gain?
For £600? The Sigma 8-16 is the estate agent's favorite. It's about as wide as you can go without gong into banana distortion fish-eyes.114Deg on the diagonal at the wide-end where it is starting to get a bit fishy. That's a £500 lens. Doesn't leave a lot for a camera to put it on. The Sggy 10-20 is a firm favorite in the UWA arena, and in many ways is probably the better lens, though only 100Deg FoV on the diagonal, and that is significant when you start pushing things that wide! Also still a £300 lens; taking half your budget though you are likely to be able to pick one up more reasonably second hand... so your budget certainly gets you into the game of UWA's, and if you were happy to live without Auto-Focus which is o great loss on a UWA, that generally have enormous Depth of Field, you could start looking at a one of the budget UWA's that are available for maybe £200 new or less 2nd hand, to leave a more substantial amount to procure a DSLR to put it on..... Doen't leave very much to start looking at flash-set ups to cover the same FoV though, or anything else....even more if you are kit swapping and want some lenses to cover the mid-range for usual photo-ops, an a long lens for those back f the room gig-shots....
The 'Here and Now' advice I have to offer, is STOP looking AT your camera... spend more time looking THROUGH your camera.
Its a big leap fro a P&S compact or i-phone to dedicated SLR photography, and I have to say that CSC/Mirror-less is not a great place to dive in; they are much more evolved 'enthusiast' cameras, which you might 'exploit' after learning the craft with a more conventional interchangeable lens 'entry' SLR... they are not interchangeable lens P&S compacts; and the systems have as many handicaps as advantages.. main advantage only being their size; down size is much less well supported systems, and hunting out lenses for them, those are likely not to be as cheap or readily obtainable, and often not have such range down n the UWA region you hope for.
I don't think that a UWA is likely a solution to the problem you even 'think' you have with the hardware you have; and tone of topic has suggested you are placing an awful lot of importance on the hardware dong the job you want, rather than you dong the job with technique... and in that, 'the photo', certainly as far as blog illustration goes, is only a fraction of it.
Back to those 70's/80's/90's magazines; or even earlier, in news-paper or book reportage, let alone photography as a whole; folk workd with incredibly limited equipment; cameras often didn't even have interchangeable lenses, let alone a range of lenses that cover even the relatively mild range of FoV of a modern kit zoom! They took stunning photo's; they illustrated stories, working with what they got. 'BIG' was shown, by displaying 'small', and implying the big around it! Impact was provided by capturing the subject or 'the moment', being selective; and working with what they had, and making that work for them, rather than expecting it to just do what they wanted... and as just a part, an illustration, of a whole, not the whole in itself, far more was made of the photo's by taking photo's to compliment and illustrate the 'Story', rather than taking a bunch of photo's and trying to make a story fro them.
Ultra-Wide-Angle, is a tempting and tantalizing arena, and with modern makers offering UWA's and at such appealing prices, even more so; and with so much consumer conviction to 'buy' solutions t presumed problems, rather than work for the answer; I struggle to recommend UWA's to ANY-ONE for very much at all... they are very difficult to get the best out of; they rarely, if ever, deliver what yo expect, especially if the notion is to cram 'big' space into small frame. But for what you suggest you want to achieve, I suspect that a UWA is even more of a blind alley, leading to likely disappointment, NOT delivering out the box, not just begging you step up to UWA photography, but more involved 'system' photography at the same time, all likely adding enormous frustrations to a job, that you probably don't really need, and detract from the one you were doing, and could probably do a lot better without any extra or resumed better kit, just by applying a bit more thought, planning, and know-how.
If you really feel you have to step up and that you must step up to UWA's whilst you are about it, and on the budget you have? I would be looking second hand, probably at entry level APS-C sensor DSLR's from Nikon/Cannon; and trying not to pay more than perhaps £200 for a 2nd hand body and 'kit' lens, to leave room in the wallet to expand that kit with a 2nd hand UWA and possibly General-Purpose longer zoom, where whats on offer will be far more important/significant than what you might like, or what the pundts say about any of it! As a toe in the water. exercise, and I would not be throwing away the compact or i-phone to do t, to see how much extra use it got... probably not that much.... and how many more photo's it gave me... less still, would suspect... and of them... how many were actually 'better' than I had before... and even if they were 'better' how much 'extra' they actually 'added' to the end result, by way of fished blog! And pondering that 'story'... how much more could be gained concentrate on that, and letting the story lead the illustratios rather than the other way around, and when shooting to illustrate the story, havig a clearer idea in conception of what best fits the story and illustrates it and adds to it.. rather than throwing words around whatever pictures you have caught along the way. Its so much in the approach, not the equipment, and so much can be made of incredibly crude equipment with the right approach.
If you feel you have to g down this route on the budget you suggest? As I know the Nikon system, my very reserved recommendation would be a D3100 or D3200; and kit 18-55, which shouldn't cost much more than £150-200. A Sigma 10-20 f4.5 could be procured new, for around £200, maybe £120 second hand, which would beg chasing better or cheaper with alternates tricky, which could get you off the stops, for about half budget, to leave room, for perhaps a 55-200 zoom, that could be procured for well under £100, and still leave a good £200 leeway for maybe a 35mm prime, which if you like the fixed prime lens shooting of the i-phoe is probably something you would get the most from; alternatively to start getting flash-guns to get the UWA coverage for 'in-doors'... BUT, all in the approach; much more t be found in the know-how and technique than the camera-bag; and scouring 2nd hand for 'best value' rather than best performance, to bring it in under-budget, it's going to be a compromise, and picking from what you can afford, rather than what you thik would 'best' do the job you 'think' you need... and back to the compromises, and whether any bit of kit will actually 'help' make a better job f the 'whole' and putting spend and time and attention into the stuff most likely to make most difference....
Yes, I don't really the zoom at all, occasionally at concerts and such or trying to get detail but mostly just take wider shot and crop in post-processing if I want to feature certain part (like feature part of a building).
