Hi Mark,
Having just got back from a week driving around Bavaria, and I must say what a great place to visit. Just follow signs to Kulmbach and then onto the Plassenburg. Park were you see a car park and walk around.
If you feel energetic then you can walk up to the castle/museum but other wise there is a bus which runs every half hour to the top.
Plenty of places to eat around the square where the show is held or further up by the fountain.
Enjoy your trip.