I'll try my best to type in what I know. If you think I missed anything you needed to read, feel free to ask again. I know I'll be missing a handful of stuff.
Anyway, since you already have 3 maids, that means you already paid off your debts.
From there, you could try maxing your Club level to 5 (max). That unlocks more venues to molest your maids on, and it unlocks the VIP events. By default, you already have 1 star on the Club level. You can increase them by:
1.)Serving more people during nighttime activities. This doesn't mean you're already whoring your girls out. Since you already paid off your debt, I assume you know what the glass of wine option thing is? It gives you money and a certain number of guests served. Once you hit somewhere around 200-300 guests, you get a star. Then you get another star at 600, I think.
2.)Getting your cleanliness/orderliness rating up. Once the maids hit 10 sessions (not days) and you get to choose if she's going to be a free maid or an exclusive one, she also unlocks new daytime activities. In particular is Cleaning (broom and dustpan), and the one with the closet and vase (not sure what to name this). If you hit around 150~ish at both of them, you unlock a star, then at 600~ish at both, another one.
After that, its just a matter of increasing your maid stats, then putting them on the Maid Test. There she unlocks new Maid classes, depending on her stats. See this link on what classes there are and how to unlock them:
You must be registered to see the links
The more classes you unlock (and level up), the more stuff you can do. You can unlock some new sex moves, and some categories like Exchange and Group play needs your maid to be using a specific class (Lewd Maid/Abnormal Maid)
