You should know your base before showing up for class. In the interview you will tell them where you want to be based. You will find your equip (if chosing a base with multi equip types) on the first day of class. If I was a commuter who ultimately wanted to be commuting to ORD I would do whatever I could to get the ERJ. QOL will be better, and shorter time on reserve as well. If you chose BOS or LGA you can put in a transfer during the first week of training when they get you set up in the computer system. Yes they are very short in ORD, so you could even get the base transfer before you finish IOE, meaning youll never have to commute to BOS. At most, I would say you could be commuting to BOS 2-3 months before getting the ORD transfer.