I can answer a few of those questions. I don't have a list in front of me so the percentile stuff I don't know....sorry
Both mdw and Bwi are fairly junior. You'll probably have good seniority at both. We carry a very small amount of reserves so I feel safe in saying you'll have a good line. There are always trips in open time or people (lance captains giving away one and 2 days. Over the winter it's more of a challenge to get premium but not impossible. During the summer it is very easy no matter where you are on the list.
As for the bases if you are commuting I'd say mdw is better. There are a lot of crashpads all within easy walking distance. There are bars and places to eat very close by...even a place I think called Mr c's...

may have been there a few times! Also decent hotel deals close by. In Bwi you either have to take the train or a cab to the pads. There are some good hotel deals though for commuters (La Quinta).
Sorry for the lack of info but I hope I helped a little bit...