I'll try to answer a few...
1. Days Off: Min of 11 days for those junior up to maybe 16-17 for the most senior. Count on 11-12 days off for most lines.
2. United Bases: IAD - CRJ, 328JET, J41
ORD - CRJ
3. Delta Bases: BOS, LGA, and CVG (eff. 5/1/02) - all 328JET
4. All new-hires are assigned a base and aircraft on the first day which is dependent on need at the time and the last four digits of your SSN. Lowest numbers get first pick etc. In the 328JET, we have had a mix of United and Delta flying in our lines for the last couple of months as we ramp up the United side in Dulles. From now on, I would expect that to cease and we should be just flying for one or the other out of our respective bases. Reserves could be sent to fly either one. There is no difference in the planes or the pay except that you have to remember to say the right airline when you thank them for flying.
Hope this helps.