| Regarding insurance, do a few enquiries, unless it is stated not valid on Nurburgring Nordschliefe explicitly on your policy, you are legally entitled to be covered since it is classed as a de-restricted toll road. German Highway laws apply, hence the no-overtaking on the right and there are speedlimits in places that you MUST adhere to, failure to do so could see you with fines from German traffic cops.
Like Ant said watch out for other traffic, the GT3 RS brigade really do fly around there, check your mirrors before and after every corner and really try to gauge how fast the car behind you is going.
A right indicator will tell them straight away you are letting them past and they should go past with minimum fuss.
Another thing, if you see a car that you think has a similar spec to yours, driving faster than you, by all means attempt to follow it's line but don't just assume because they can corner at that speed that you can too! Knowing the track is everything there so get a map and start learning. There are warning signs on the major corners that will catch you out but try and learn where they are in advance so you are ready for them.
Also watch out on the Karussel, it's easy to get carried away and end up sideways on the exit, it's a phenomenal cornering experience, but it's also easy to get it wrong.  | 
