Roach has apparently said "I like the kid and he's keen so we're just trying to get something sorted out with his people." So failing a negotiation screw-up, which you can't count out, it seems a good chance this will happen.
Well that's a start, because Amir is a difficult person to like. I don't see this working out though - Roach likes to have an influence on his fighters and seems to genuinely care about them. Warren will want Roach to take his 5% and STFU.
Roach and the mayweathers were the best options. Roach worked with Toney for a long time, im pretty sure he knows a thing or two about training in defense. Khan is also a fast explosive fighter simmilar to Pac, in which case Roach will just have to focus on the defense part of the training.