Sorry, no idea on the watersports mate, I've only ever seen the sea in Pattaya from the baht bus as I go back to walking st from soi 6
If its diving your after though I think you'd be better off in Phuket than Pattaya.
2 girls at a time isn't a problem although its a bit trickier if you want the girls to get it on together too. Just ask around, have a chat with the girls or mamasans and explain what you're looking for.
As for bringing a girl back to the UK, I don't even want to be here myself so I wouldn't want to inflict it on anyone else
I'm working on staying over there instead.
I always stay in a hotel but a mate usually rents a villa in Jomtien which is really nice but far from cheap, depends on what your looking to spend.