Sounds great! Take the time you need, ain't nobody wants something rushed lol
As for "how deep"... First, as a disclaimer, this is *purely* a personal opinion lol
For one, I am personally not very interested in seeing the main character pee on.. anything, really. But, I know some like that, so if you want to cater to a wider populace, probably good to include some. Peeing on the dolls is a good one, having them drink it is also solid.
I would personally love seeing the dolls peeing a lot more, and especially in lesbian ways. Having one doll pee on another, having one doll drink anothers pee, etc, would be fantastic stuff.
I am pretty sure I saw something about doing doggy play with teh dolls too (leading them around on leashes and such) and including peeing there is a great option as well; type, taking them on "walks" where they pee on things with a raised leg, like dogs.
One interesting possibility could for example be, forbidding them to use the toilet, and then watching them try to deal with that via the cameras. Examples of "endings" for that could be, wetting the bed, trying to pee in a flower pot, wetting their pants, getting bratty and pissing on the main characters bed/floor, or even pissing out the window or something. Depends on what you have animations/poses to do of course. Anything that isn't a toilet or sink would be great IMO.
And upgrade to the dolls to make them pee something tasty wouldn't be bad either. Energy drink, maybe?
Feel free to PM me if you want to throw ideas to see if it's interesting, or anything like that!