I'm in Berlin in a couple of weeks and fancy dipping my toe in to an FKK club for the first time. A couple of questions if that's ok?

I'm staying in Alexanderplatz, so will probably get the S-Bahn going (about 7pm)
If I leave Artemis quite late (10,11,12), is the S-Bahn pretty safe or would you recommend a taxi?
I've read a few reviews and realise you walk around in a bath robe.
How do you pay the girls or buy beers and is it cash only? Or can you pay by card?
Finally, if it's cash, how much would you recommend taking if you had fun with 3 girls and had a few beers?
Cheers
