I'll get both the dock and the lens.
So any general tips for shooting in the Mara?
Clothing wise, will cargo trousers, and a jacket be ok? Any reason I need to wear beige/sandy colours...?
My mains tips would be set your gear and as far as possible forget it. Just check the exposure on the screen as you go. Most of my shots are f8 AV and if I need more shutter speed I up the ISO, but that's only early morning. It goes from dark to light quickly and same in the late afternoon/evening. You can judge after the first drive and adjust as needed. Much better focusing on spotting than playing with gear. It tends to be the case that a closer shot is more interesting than one of a critter in the centre of a vast expanse, but you will know all that composition stuff. Aim for the eye mainly. Consider you can always crop later so build in some crop space as necessary. Unless you want 'a record' shot then only click if the shot is worth having. Big cameras shooting off machine gun style constantly can be very irritating. Focus on steadiness and composition and take it slow rather than spray and pray.
The guides are normally very good, but they will often ignore animals or birds they see every day. For you it's the first time and you may not get another chance! Things like Zebra, various buck, whatever are common but still photogenic! I have several times forgot to check and ended up with over-exposed shots after the first hour or so early morning. The stop down is because 99% of lenses I've ever used perform better ... OK, 100%! The extra DOF doesn't hurt. At distance bokeh is usually fine. On public drives, you are either going to have good spotters and drivers or average. The good ones know how to position the vehicle and light.
Cargo trousers are good. I usually take 3 shorts, two cargo type trousers for a 3-week trip. Mozzies can be an issue evening time so you need to cover skin. I would buy a anti-mozzie roll on or cream. Use it at all times, esp around ankles but other exposed areas too. In dry season it's far less an issue. I normally go July or August and it's effectively zero issue, tho dunno Kenya/Tanzania. You can also get burners for night time. Depends on the local area. You don't normally need many changes of clothes as most people don't sweat much as it'll be dry heat. If you can find out about laundry in camp then do so as if available then you can pack even light. Sometimes workers will wash clothes as it's extra income. They may have a washing machine, or they have a handy rock and rive! Don't take your expensive clothes! Take a fleece and I prefer short sleeved sleeves that don't crease during the day. Rohan are very good all round for travel if you pick wisely. You can pack a couple of t-shirts for evenings to wear with your fleece.
Drink lots of water. Go to the loo before each game drive. I'm usually out 3-4 hours but your guided ones may be a lot shorter, so less important. It's not like you can stop and go behind a bush! It's tricky if you have a weak-bladdered type amongst your party! Whatever you wear should ideally be unobtrusive, but you have no control over what others wear on public drives, so moot. I personally prefer clothes that blend in. When I go it's pretty much all dry, so beige, burn orange, grey type colours. It's nice to take coffee or tea out with you in a small flask and an energy bar for breakfast.
I like to take laptop and backup drive. After each drive, I check shots, store the keepers, backup, junk the rest and reformat. It's quite nice to share shots and it passes the time amongst a group. We normally have a bit of a fun competition after the first week or so. An easy access bag is good for drives so everything stays tidy and to hand and it will offer some protection from dust. Not needed if you have the one body and lens per person. Binoculars are good, say some 10x50. It's worth spending if you want a good pair to last, but for once off use not really. Sometimes you just want to spot rather than shoot.
This is the get up I have recommended to people on my trips, day and evening wear, tho I don't take the vest anymore. It's handy but I like to travel as light as possible now:
following my nose wherever it takes me each time. Do take a sun hat!