Y1, Y2, W and X are where I've had tickets directly from OSU previously.
RE: parking: The stadium is surrounded on 3 sides by campus and the 4th by a residential neighborhood. If you're lucky, you can find a spot at the hospital garage or other campus garages (there's no huge fields like you find at OSU, PSU or UM). Best bet is to park downtown and walk. State street is closed to traffic and has lots of bars catering to pregame crowds.
Tailgating is different in Madison - it's bars and house parties because they don't have the aforementioned huge lots and fields that promote tailgating. Should you walk down state street, just bar hop until you get to the stadium. Worst case you eat a lot of brats and cheese curds; best case you eat a lot of brats and cheese curds.