Just to add to the malaria tablet advice... go get a jab. Do yourself a favour and avoid tablets. Apart from tasting awful and requiring to take them habitually, they come with an insane amount of side affects for a good fraction of people. Side affects can be from mild nausea/diarrhoea to severe enough to ruin a holiday. Considering the money you are putting forward, dont bother with tablets.
That's why you take malerone.
Is the jab cheaper than Malerone? If so then I'll have to look into that for my next trip.
Haven't done anything in Kenya or Tanzania but have done stuff in Botswana and Namibia. Chobe national park (Botswana) is ok, the river is nice but there are just too many people. This may be the same issue with Kenya and Tanzania as well. Etosha in Namibia on the other hand was stunning. Loads of wildlife lovely and quiet. Definitely worth having a look at before booking.
Also if you want something a bit different you can look at Gabon and Petit Loanga. A slightly different safari experience, where most of your safari will be done in a boat or on foot. The wildlife is a bit different too, things like forest elephant rather than plains elephant and no big cats but there is the chance to see gorillas. it's a pretty unique experience as you're hiking through the forest, not just plains. I didn't go to petit Loanga as we didn't have the budget to stay there, we roughed it a bit and went slightly farther south and stayed in a community run place instead (but the same Loanga park). Your money goes a lot further for things like transport and guides though. We had a huge boat, driver and two guides for the week we were there (4 of us), and we're pretty much the only ones on the water.
May be worth doing the traditional safari experience first though as you will see more animals.
One thing I would recommend anywhere is to do as many walking safaris as possible. Being in a car means you can get closer and cover more ground but there is nothing like walking through the bush and actually being at the same level as the animals. It's a totally different experience.