Agreed, for specific questions about ORD, post in the Chicago forum.
Wednesday night will be a normal night at ORD, not particularly busy like a Thursday or Sunday night. T5 is of course a separate building and you'll need to go through security again, so if you have a short connection time, you will need to hurry. There's a train between T1-3 and T5.
I don't think anyone can answer the question about seats two weeks out. My favorite tactic is to approach the gate agent, smile and be friendly, and ask if there's a seat that's likely to go out with an empty next to it. Probably my imagination, but I like to think they remember not to automatically assign that one to a standby unless it's full.
