Let's not fanny about now. Just be sensible, you aren't going to set any lap records. Your first time out there will be terrifying but you'll get over it. TF days can be a mad one but if you respect it you'll be fine. Let the M2 and GT3 RS pass you on the left, keep your wits about you, you'll live in your mirrors for the first time checking the next 911 that's rogering up behind you. This is the same if you were in your own car or ring rental.
If doing a lap really isn't for you, then as mentioned there is plenty to do. Head into Adenau and have a mooch around, sample some very good food and a Bitburg or two... head up the embankment opposite cockpit and spectate. Head up to Devils Dinner and check out some of the bits of metal as it cools down from its lap. There is plenty to do besides doing laps but mainly we all go there to do laps, lets be honest.
Rent4Ring I think it one of the more reasonable options to rent from with the many swifts they have. If you aren't afraid to get talking you may be able to jump in with someone which might be an option.