I would go for a petrol car rather than diesel, since I believe it to be more commonly available, and easier to work on at the roadside. For similar reasons I’d opt for a manual rather than an automatic.
A couple of things with fuel and car choice:
Petrol quality varies a great deal from country to country and not always of a suitable octane rating.
Petrol is much more volatile and of a greater fire risk.
More components in the fuel and ignition systems likely to give problems.
Water crossings will kill it more quickly.
High altitudes will seriously reduce performance.
Diesel is a much safer fuel.
A lot of the roads in remote areas see a lot of diesel trucks, so fuel is more readily available.
It is possible to get low quality diesel, but a diesel engine will cope with it better, as it will with high altitudes.
Less, albeit it essential, parts to maintain in a diesel system.
Water crossings do not bother it, more so if you fit a basic snorkel.
Because of the truck scene more likely to be local help familiar with diesel engines.
Transmission: most definitely manual.
An older 4WD that does not depend on modern electronics to run the engine. Unless you have some form of fault code reader, and know how to use it, modern electronics will eat your lunch!
There are plenty of used 4WDs available here, but a lot of them have had the engine replaced with something out of a Jap wreck. Try and stick with something that has its original running gear. You do not have to be a qualified mechanic to work on them, but should be familiar with how things work and use basic tools.
Just my opinion based on years of operating these things.
