y'know, this just occurred to me, and pardon if I'm being rude - at his size, will his belly make it difficult for him to reach the drops, and thus the bar end shifters? And/or does he have back issues? Bar end shifters might not be the best idea for someone who can't lean very far forward.

Re: frame materials, I've known two very large guys with carbon frames who've had no problems at all. Wheels and spokes, yes - frames, no.