It's pointless going to Oase for only 4 hours, the idea is to spend a day there, why pay 50€ for a taxi, when you can get a S-bahn to Friedrichsdorf then short taxi ride to Oase. And I don't understand why someone goes to Germany for a outcall, it's like going somewhere where there are great restaurants, and wanting to eat takeaway in your room, the great thing about going to a club, is you see all the girls in the flesh, literally, as they are naked, and have your own time to pick who to go with.
As for airports, Hahn is the budget airport that Ryan air flies to.