The thing you worry about with Alston is whether he'd accept a backup role. Alston has never exactly been a leader in the locker room, so bringing him in could be a feast or famine type of move.
That's my concern too, but I think every team interested in his services will give him a backup role, except for Miami. But every other contender will offer him a backup role so it shouldn't be a problem for him if he wants to win a ring.
But like I said, I don't see Danny offering him a contract, although I think he should. And I'm not sure Rafer would get along Eddie and Rondo.
As for the problems in the locker room or off the court... we did well with Marbury and he went absolutely crazy the following summer, when he was no more a Celtic, so I think Rafer wouldn't be a problem. And in the worst case, you can cut him.