I've been twice (61 laps now).
The Z is a very forgiving car designed to be driven hard, so check your oil and tyres and go for it.
I chunneld and drove (in convoy). Allowed 10 hours from Oxford to Nurburg including Shuttle wait times. Format was drive out day one, day two and three drive the Nordschleiffe, day four drive home (in time for afternoon tea!).
If you'd like any more details, PM me.......