Hi Jonny
I assume you've read the reviews on Rios in the Clubs section.
We were there last Saturday night and had a great time. We met some nice couples and although it was quiet, there was plenty of action. I've only ever been on a Saturday night, but I think that regardless of the time, it's better to go as a couple as opposed to on your own. As a couple is the only way you'll gain access to upstairs.
As for downstairs, there are a lot of single men milling around hoping for a piece of action. There are also some very nice nude or semi-nude women, but they all seem to be partnered up. You should enjoy the facilities though. The jacuzzis, saunas and the pool are great and the staff are really friendly.
You really need a partner to go with though! Good Luck!