I went in October 2012, it was one of the coolest experiences of my life.
-I'm not sure about a bus or train, but I think in my research I found that the easiest way to get to the area was to rent a car. Plus, you get the experience of driving on the autobahn, which was also one of the best car related experiences in my life. So orderly and non-infuriating when slower traffic always moves over for faster traffic. We left from Frankfurt (which conveniently has a non stop flight to and from Houston), and it was less than 2 hours drive. The rental car is also nice because the ring is surrounded by small towns. There's not a whole lot of public transport, so it is easier to drive. We drove to different towns for dinner and went to the Nurburg castle.
-I also rented a track prepared Suzuki Swift from
http://www.rent4ring.de. I wouldn't worry too much about what type of car you drive...I wouldn't be able to even approach the limits of any car the first time out. It's quite scary with expensive car after expensive car passing you haphazardly when you're just trying not to crash into barriers and guess which direction the next turn is in. The Swift was lowered, stripped, and equipped with sticky tires and was actually really fun to drive, but I personally love FWD hot hatches. There's just a non intimidating puppy dog fun factor to them. Not much worry about spinning out if you give it too much gas or go into a turn a little hot.
-I'm sure you've read about not driving a regular rental car on the ring. There's no insurance that will cover any damage, and rumor has it that rental car companies monitor the ring to see if someone drives one of their cars onto the track. You can decide whether or not to do it, but for me the risk wasn't worth it. So yes, I rented two cars...one to drive to the ring and another to drive ON the ring. rent4ring provides you with some amount of insurance, but if you take out some crash barrier, you'll definitely have to pay out of pocket. Just don't crash.
-There's a calendar on the official nurburgring website that tells you which days the track will be open for tourist driving (Touristenfahrten). Make sure you keep checking, I hear the calendars can change with short notice if a manufacturer books the track. Also hope for good weather, I got lucky with a beautiful sunny day.
-All in all it was pretty pricey to rent the Swift, pay for laps, regular rental car, hotel, etc, but it was totally worth it. I can't recall how much exactly everything was.
http://nurburgring.org.uk/ That website is British based so it is all in English, and it has a wealth of information along with a calendar. It was instrumental for me, read through the whole thing.
Any other questions, feel free to ask.