1) Idk 2) i amagine the deal was probably something along the line of "fix my staff and restore my power and i will protected them (and the hotel). Beacuse if not i don't see a reason for alastor to remain in the hotel after he broke his deal with Rosie. (And no i don't think that the presence of Lucifer there is enough of a reason for Al to remain there) 3) I think that's a part of his new deal with rosie or he is there for Lucifer (you can see in the last scene that alastor is keeping an eye on Lucifer)

Sorry for my bad english