Hey Mike
First of all, welcome here, we really appreciate it to see also english speeking guys in our community!
To come to the festival from munich you might either take the train which takes about an hour or you rent a car.
But I assume you take the train, so first of all you have to get to the central train station of Munich, which is one direct line from the airport and takes about an hour I think. Then you take a train from Munich to Nuremberg. From there u take a shuttle to the park and you're done.
The best place to get beer will probably be Munich because i assume that a lot of people will want to buy beer in Nuremberg. But if you have any possibility to buy beer in austria I would recommend you that because its cheaper there and you have to pay no mortgage.
If you dont have the opportunity for that then don't worry about it. Its not that expensive. You can get it in basically any supermarket so you should be fine.
Enjoy your festival,
bernd