Hi Vivienne, welcome to 3dxChat!
1. There are a few "official" rooms (Sin Club, a beach, a beach club, a yacht, Fresco Club, Old West scenario...) always available. Some have usually a good number of players, others are nearly empty.
Then you have the custom built rooms, shared by players. Usually there are several dozens of shared rooms, ranging from 0 to more than 100 players in. Some of them are amazingly built (using the in-game World Editor), some others are modifications of publicly available rooms. If you can see these rooms on your list, it means you can go there (some rooms are only shared among friends or groups, so you may not be able to see/access them).
You start with the default apartment. As mentioned above, there are some sites that share some rooms for download and use (many are free, some aren't). Some of the most popular: https://www.3dxchatsharing.com (no register required), https://3dxmodz.com (register required).
2. Some body details are adjustable but not to extremes (far from that). Avatar height, vagina and penis size are not adjustable. Limbs are adjustable in thickness, not length, Chest and butt sizes are adjustable. And a lot of face characteristics. Some tattooing too, not much. And some appendixes like wings, ears and tails (not much as well).
3. Contrary to other games, all available dressing stuff is free and available for use. Also contrary to other games, variety is not awesome (far from that). There is some casual stuff, but the majority (at least for women) is quite sexualized.
We are waiting for a significant update during the next few weeks with some new stuff.
4. You can't transfer money (XGold) within the game and there are no organized escort services. In reality, there are no "real" escort services at all. Of course you can say you are an escort and you want to receive "gifts" for your services (it's common to see profiles asking for 1 gift for 15min, 2 gifts for 30min, 3 gifts for 1h or something like this) but very few players give it much importance.
XGold, the game currency, is not very useful. You can use it to buy gifts for your friends (it's just a symbol with an added text) [cost 300 XGold], to create new avatars (you can have up to 3 with your subscription) [cost 10 000 XGold], to change name or gender [cost 20 000 XGold, even you only change one of them], to marry [cost 10 000 XGold to the "proponent"]. When you pick a bottle of beer, it announces a cost of 35 XGold but nothing is charged. If you login every day you can collect nearly 10 000 XGold in one month (300 per day)
You can find videos on Youtube about avatar customization (body and dressing), building using the World Editor and some existing rooms.
I hope this helped making you more willing to play