I figure, if I build one, I'll go with two channels for throttle. The main throttle will control the nose motor, while a secondary channel will control the outboards. I doubt the Trimotor will really need much in the way of differential thrust to steer effectively, especially not if I fly it scale. I do think I'll increase the ailerons a bit from the scale size, as it's easier to program out too much aileron, than it is to work with too little.
I've been doing some old-school sketching on graph paper for a Trimotor with a 49" wingspan. I don't have any of the computer programs for creating plans, so I won't be able to easily upload anything I come up with yet. If I do come up with a workable design, I'll see if I can scan it, so that I can post it here.
My designing so far has been pretty limited, and often involves some Edison-style bulldogging a problem. Thomas Edison was a tinkerer, who would keep trying different approaches to a problem until he found a solution (as compared to Nikola Tesla, who worked with theory and mathematics to find solutions. If the two men could have managed to get along and work together, I think they would have been an unstoppable team, but they couldn't stand each other). When I built the wing to replace the destroyed one on my Sensei, I started by making a wing profile with a 1" strip of foamboard, to check my measurements and how it went together. I figure I'll do a bit of that this weekend for the Trimotor wing, and see how it looks.