You are either home based, or in one of two smaller special programs with bases in LAS and IAD.
Most lines will be reserve lines, there are a few lines of actual rescheduled known flying, with several from SEA. Holding them is an issue of seniority as they do not seem to go junior. The LAS goes junior on the FO side.
everything else, including most of this, has been discussed in the two Omni threads. It has not changed much except for the hiring process, so spending some time reading the threads is highly advisable.
Its a great place to work

To answer your specific question. You can change your “Home Airport” for home basing every bid cycle. You can also do alternate travel in most cases. Basically, if the ticket your asking for is cheaper than your home base airport, you’ll typically get the ALT travel as long as it won’t impede any duty time.