Thanks for the great feedback.

Colombia does litteraly seem to be the showstopper: there is 150 km road missing from Panama to Colombia... (according to the Colombia Lonely Planet). I'll focus on Central America first then next time I'll buy a diesel LandCruiser in/for South America.

Besides that - Colombia really isn't very safe. I would do it as backpacker and travel by bus - but with your own vehicle you attract a bit more attention.