Weather...
You will be sorrreee! To get caught in cloud trying to dodge African CBs by peering at the crappy little radar in a light twin.... Are you mad? (No probably just young and optimistic, but to learn from experience you have to survive the experiences.) The weather is far more powerful than a light aircraft and diverting, or simply sitting out the bad weather, will prove the way to go.
I was with a guy who flew into a humble cumulus cloud in a C-310. Moments later, as we were getting a thorough kicking, he said, 'What to I do now?'
'Back up, and go around the cloud!' Durrr...
It is a funny thing, but if you look in the books you can see that the power-to-weight ratio of the C402C is superior to that of the C404 at max gross. Too, the C404's GTSIO-whatever engines demand consideration if you want to make TBO, when the aircraft has no cowl flaps. The very similar TSIO- engines of the C402C are simpler, and thus cheaper, I bet. The thing is, imagine a hot day and a heavy load and a short strip with trees out there past it... You have to ask yourself, 'Do you feel lucky, Punk? Well, do you?'
A glance at the numbers on a web site for a C340 shows that it needs about 3000 feet of asphalt for accelerate-stop. You want to operate off a shorter dirt strip? So, what is the plan B when you lose one engine at about 50 knots? You might want to back off and re-think this one. Safety costs money, but just about the time you find yourself in some terrible mess you would gladly spend the extra for turbine engines or at least better performance.
We had a real nice kid from Iceland who wanted to come to work with us in Nigeria. He was too low-time to get the job so he went back to doing air ambulance in an old Seneca back home. He got caught in a mountain wave or something, pulled down into terrain that old airplane couldn't out-climb and that was that. Hearing that sort of thing tends to stay with one, just like seeing, first-hand, the single-engine performance of a rather average C404 with a full load off a short strip on a hot afternoon in Nigeria. All that happened was that the big hose popped off the intake manifold, but it did that at about 8000 feet. If it had happened just at rotation, well.... Bob Hoover might have got away with that, but I am not Bob Hoover.
Even if you think you want an African adventure, the flight nurse and the patient did not sign up for that sort of a ride. Too, if things do go all pear-shaped, and if you survive that, expect to have to answer some very hard questions such as, 'The book says you needed more than 3000 feet of asphalt. You chose to operate off a 700-metre (popular number, about 2300 feet) unpaved strip. Why is that?'