Experimentals rock in Africa
I went through a similar calculus and ended up building an experimental and importing it into DRC. Even with a mogas STC you technically can't do much beyond fly your airplane and change the oil if you are not an A&P. And hey, just because it's mogas does not mean it is mogas in Africa--watch those octane numbers! My Rotax 912UL hums along fine and I can maintain it myself.
I know that there are experimentals in many of the countries you list--Zim and TZ and KE for sure, and DRC just loosened up (a little).
The biggest issue I faced with getting my Zenith CH701STOL in the air was actually finding insurance. For E Africa you will find policies that cover many countries, nice. Also, you may find that some countries require an HF radio, a hassle but it can be done. And keep in mind that you will never have a full picture of fees until you actually show up.
Good luck!