Why those lenses? Neither of them are particularly good for most wildlife, and neither of them are particularly good for macro.
Why exactly do you want to go to a full frame camera? What do you think it will do for you?
I know that. I have the Sigma 150mm-500mm and the Canon 100mm Macro lens, both are in my signature.
My top priorities in using the camera for is 1) Landscapes 2) Macro 3) Wildlife i.e. deer, large/small birds of prey, garden birds 4) Whatever else may turn up.
The other main benefit of fullframe is if you reall want to get the full background blur of fast f1.2 and f1.4 lenses for portraits. I noticed that your using the 450D, I still have that camera and hate the sensor, so I was amazed at the quality of your landscape shots in your Flickr stream. In terms of value for money and biggest bang for your buck the 77D is my recommendation.
There are times when I would have wanted the background blurred out more such as in the shots of the Hummingbird Moth, and flower images....and thank you. To be honest, I think the landscapes could be more in focus, as for the birds (the hooded crow and mandarin duck), I'm not keen on them. Maybe it's down to user error (no tripod/monopod etc) or something else.
Other answers to questions
The Sony A9 is too expensive and out of my reach. To be honest I'd rather stick to Canon and go for either the 6D mkII or the 5D mkIV. I've scanned the internet for wildlife shots taken with the mk IV and they appear to be excellent.
I would like a FF for low light and have a higher range of ISO, and since I tend to shoot HDRs mostly, I think a FF will enhance the capabilities that my crop sensor cannot maintain/achieve.
Able to print larger images.
I hate how grainy some of my images are. I use Lightroom to process all my images. I take the grainy-ness out then
sharpen it and I'm not keen on how the images turn out as I don't think they appear sharpened.
As for added weight - If I can carry my Manfrotto 055XPRO tripod without using it for 4 miles (last distance I walked), I'm sure I wouldn't have a problem with weight. I'll be upgrading to a carbon tripod in the future.
would be to get the additional magnification on lenses for wildlife photography... but then again, I could probably just crop in on a FF shot instead.
That's what I was thinking too.