Is 7,500$ enough for 4 months in Africa?

US dollars?

4 months for this route is pretty quick,if its all overland.You are going to be moving fast....

Apart from your activities,accommodation and food...at lot depends on which countries you stay longer in.South Africa is more than double the cost of Ethiopia for example.

Still,7,500 for 4 months works out at $60 a day per person....it should be plenty if you travel as a backpacker.Organised trips and safaris are the things which really push costs up....

Yes, it's US dollars. (wich it is converted into, from my local currency wich is the Krone from Denmark)

We are moving fast into Zimbabwe after only a couple af days in South Africa. We will spend the longest time in Zimbabwe, Malawi, Kenya, Ethiopia and Egypt.

Then it should be plenty....you can live well enough in all of those countries on $60 a day,per person.

More expensive would be South Africa,Zanzibar,Ruanda (if you want to see gorillas).

The safari in Kenya is going to set you back, as is the diving. But generally speaking you should be ok - though it is going to be quite rushed. Be warned that getting the Sudan visa in Ethiopia can be a hassle and you may end up not having the time to hang around Ethiopia trying to sort it out in which case you'll probably have to hop over - a shame but with your time frame you don't have much flexibility.

Your budget sounds about right to me. As someone mentioned, if you only sleep, eat, travel round, then you'd be fine, but be mindful of organised activities and tours, as the safari, which are quite deer. In saying that, we did a 3 day, 2 night safari in the Maasai Mara in Kenya for (if I remember correctly) US250 per person including all entrance fees, food and accommodation. This was rather the bottom end of the price range, just to give you an idea. I don't dive, so I can't comment on that, but from what I've seen diving isn't cheap :)
Have fun!