KingDavid: My biggest question is whether to change my seat from the rear of the plane or not.
No contest here: Change your seat to one further forward. First class seats are always nicer ...
Seriously, though, it is usually quieter up the front and therefore less tiring. If you're near the front of economy, you may well be over the wing and therefore moving about less than if you are near the tail. All in all, it's usually better further forward, which is why they tend to put the premium classes towards the pointy end.
If you happen to find that you are disembarked onto a bus at IAD, then just stay in your seat. Let everyone else walk past you. Flirt with the cabin crew. When the bus is ready to go and you're about to be lynched by the people who've been hurrying off, then it's time to get on the bus and stand next to the driver.