If I tell a recruit I'll redshirt him next season and he says he wants to play but signs a scholarship anyway, how will he react if I redshirt him?  Is informing him enough or should I expect him to transfer if I do redshirt him?

Since he didn't reject the scholarship he will most probably be fine. If he is unhappy his WE will drop, maybe a little (I just had an unhappy WE go from 99 to 89), but usually it will drop a lot. If it does drop so much that you regret it you can always remove the redshirt and his WE will go back up. Just for the heck of it you can then try to redshirt a different player. And another. etc.

If you kept the inform of redshirt on and he signed then you can redshirt him no problems. If you took the inform off then that is the same as saying you agree not to redshirt him.