start by adding together how much total weight you are going to be hauling around. avoid the situation where you are overloaded = breakdowns on the road.
Now when prepairing for my own trip I have noticed the value of driving the car enough before going to show up any faults. Of course the car has to be tip top and all those parts replaced that are know to break up with miles (joints, shocks, alternator, starter...good C-rated (van) tyres...)
the second thing, there are few vehicles that are favored by overlanders, the choice is personal since both have stong and weak points....just be avere if you need an carnet De Passage document, valuable car can add up in carnet value significally
thats why many overlanders take cheap older vehicles.
the best book for the subject that I have read, Overlander Handbook, by C. S.
it is not the destination, it all about the journey...
Capt, Jack Sparrow