There's some great info on here already and have read most of it. If anyone experienced has a better city i should be visiting or plan let me know! Not sure where to stay and time/days to go to each club.
I have only been to 1 FKK, Sharks (on a Sat night) and what a experience it was

About 100 SP, most of them topless strutting about. Surprisingly, the food is also very nice as well.
Berlin is a much better City than Frankfurt and there is loads to do other than punting. Berlin also has Artemis, although slightly more expensive for entry €80 (or was) and €60 30mins Basic punt.
Whatever FKK you go to, watch for the SP asking if this is your 1st time as they will up-sell and advise you it is €100 for 30mins (certainly for Sharks and Artemis from what l have read). Just advise them you have been before

and that you only go to the room for €50 with OWO (if that's what you are after) otherwise they will lump on €50 for the OWO.
Either option, you will not be disappointed.