I've been to Frankfurt a few times but I've never ventured into any FKK. I'm happy enough getting my rocks off in the RLD before hitting the pubs. I enjoy walking up and down the stairs and checking out the birds. I've been to Prague FKK and I wasn't really impressed, so that's put me off visiting the German ones. Besides, a holiday for me is as much about drinking as shagging and the RLD has both in abundance.
I never went into any strip clubs. I'd be more inclined to go in if the bouncers and touts weren't so annoying. It isn't a good advert for the place having some arsehole grabbing your arm when you walk past. I've asked on this forum before about strip clubs but didn't get an answer.
Regarding Frankfurter sausages, they sometimes have a load of stalls set up on Kaiserstrasse selling all kinds of food and beer. I spent a relaxing afternoon last year sitting in the sun drinking and tucking into hot dogs. I'd recommend currywurst, which is a chopped up Frankfurter in curry sauce.
Aside from the Thai pub that I mentioned earlier (I had a closer look at the photo and I think it says massageplanete Elbe on the sign) there's a few other good pubs in the area, though I can't remember their names. There's one in particular on Kaiserstrasse (just outside the RLD) that I like. In the evenings there's usually a streetwalker or two hanging about across the road. It can be amusing watching them come and go while drinking a cold beer.
I prefer Frankfurt RLD to Pascha as everything is within walking distance and you have a variety of pubs, restuarants and so nearby. Pascha is quite far away from Cologne city centre and there isn't really anything interesting nearby. You also have to pay a fiver to get in, while in Frankfurt you can walk in and out of the brothels without any problems.