They walk you through the filling in of the permanent bid sheet either the second or third day of training if I remember correctly and you will know where you are based before you finish systems training and probably before you get done with indoc. It's possible your status can change more than once before you even get out on OE depending on the movement.

My opinion is that if you are going to commute, then DCA would be the best place to be on reserve at. There are crashpads within walking distance to national and lots of stuff to do on your down time that still keeps you within 2 hours of the airport.