It was open in 2011 as well. They opened the doors when they said they would.
My advice is to get there early. Don’t worry about being at the front of the queue, that isn’t necessary, but somewhere near the front is advantageous. We didn’t meet any drivers or anything like that, we were too busy being mesmerised by everything else. However, if that’s your thing, stick yourself directly outside the garage as central as possible and pester as many people as you can to see if your preferred driver will actually make an appearance. It’s not a guarantee and they do stress that.
All you need, like @helixios said is a weekend ticket.
I wasn’t aware they did it at Spa, I’m going there this year.