I'm no pro at this, but I'd have to say (from my reading here):
1. What is the best FKK? Clearly they're all different, but if you want the classic parade of bodies and couch-action scene, your best bet is probably Goldentime, which is only 10km past of the Dutch border at Venlo. If you want a more relaxed experience, I can personally recommend PHG as can many others. I can't compare it to Bianca, but it was generally pretty good, and it has Sammy. I hear quite a few superstars make a circuit of these two places. PHG is also out through Venlo, but a longer taxi ride is required (about 30km).
http://www.planet-happy-garden.info/
http://www.goldentime.de
2. What is the best way to get there? Again, depends on the schedule - a train from Amsterdam to Venlo, the common waypoint, takes about 2 1/4 hours, and then add in the car ride.
3. Train schedules: The big problem with making it a day trip is that these places close at 1am, but your last train from Venlo is at 11pm - so you'd have to be out of there no later than 10:15pm, to be back on the same day. There are hotels in the area and in Venlo. The first train back in the morning is 5:50 am, and that gets you to Centraal Station at 8:15 am. If you want to have breakfast first, leaving by 9am gets you in CS by noon.
http://www.ns.nl/
You can play with the train schedule in English too - the English button is near the ZOEK box.
Driving is easy if you get a car with GPS navigation (blissfully easy, actually!) but otherwise keep in mind that the Dutch don't use the usual US-employed grid system for laying out towns. Without a GPS you could be driving in circles awhile.
