Its up to you how early you want to get there. Doors open an hour and a half before gametime. If you want to get there earlier you can. I know there will be both grad students (Wallace Wade side of Cameron) and undergrads (campus side of Cameron) there well before that hanging out and having a couple adult beverages. Parking is usually 5 dollars. If you get there early, the lots on Towerview may still have spots, but after that, you'll be stuck parking at either the Bryan Center or the Circuit drive lots. As far as before the game, most students are in line for a while hanging out. After the game, theres no defined places. I usually either hit Armadillo Grill on campus or Devine's/Sati's/Federal/Alivia's on main street.
Atmosphere in the "above the rail" section varies game to game. You'll be sitting down most of the game though, unless the students tell you to "stand up".