I would start w/the 40% and work back from there.  The thinner it is, the thinner it will lay down and reduce the orange peel look, which will help with the final steps.

The door jams will be easy since you will be using a foam roller.  For between the cab and bed, just unbolt the bed and slide it back an inch or two, you shouldn't have to remove it.

You will have to sand off the clear coat, or the new paint will flake off as the clear separates from the base.