Fuel/range availabilty
You didn't state whether your aerie will require Avgas or JetA1 ?
That makes a huge difference ! As does it's range !
With JetA1 you can route from Johannesburg via Kasane, Ndola,
Lubumbashi & if your range is sufficient , then on to Kinshasa.
There was JetA1 at Kananga last year[ almost halfway].
Avgas is very scarce- so you'd better check very carefully & be
very sure that it's really available on arrival !
The Medical flights know how to obtain this info.
Good luck.