As Patrice mentioned, the Touristfahrten is simply open track times, you pay Der Ticketmeister and he waves you out onto the track. No orientation, no safety briefing, nothing. You'd think they would send you to a pit area to check your car or take out some loose items, but once you get past the ticket guy, the track is right there!
Not sure if they still do this, but when we went, we paid to go through the Nurburgring museum right at the track. It wasn't until we were driving away from there that we noticed that the museum ticket stub was good for like a 50% discount on a lap around the 'Ring!!

I wouldn't get too hung up on having an "E36 or better", IMHO, you'll have a blast in anything with wheels. The track is SOOOO long that it would take a couple of years of driving on it to remember every turn in and apex.
We took a Nissan Primera out there, sort of like an Altima or Stanza or something like that. I believe it was a 2.0l 16v, and it was a blast. I frankly would not want to be out there for the first time with something with tons of HP.