I think this was addressed earlier, and if anybody else out there remembers please point out the particular thread. That being said:
1: ACA has thousands of applications on file, and I seriously doubt if they are going to waste training time and money on someone who might go back to another airline. No offense, just business.
2: Base depends on which aircraft you get, and that itself is random chance.
a) J-41's are only at Dulles
b) CRJ's are only at Dulles and O'Hare - with everybody seemingly being assigned Chicago as of late.
c) FRJ's are in LaGuardia, Logan, and Cincinnati - expect to go to either Boston or Cincy.
I am very pleased with ACA. Work rules are good and the commuter policy is outstanding (you just have to list on 2 available flights - if you get bumped off, you are covered.) The company is doing well and is on sound financial ground. Good Luck on whichever company you choose.