Don't stress bout getting your prefs, they don't take rolls or anything and they are nowhere near full so you can really turn up to any one you want (or just not go at all!)
Yeah when you get there you line up in Surname groups and they give you your personal timetable, then you go to a session in the big auditorium where they try to sell the uni to you, and then you go and have something to eat and attend some lectures, then lunch and a few more, then home.