It's mainly to keep out those folks who can't handle the cunny, and were reporting the site to the webhost. As for how effective that is, we shall see.
Lately they've been working on using Stable Diffusion to generate AI art on the fly based on your slave's descriptions, but it needs a lot of set up, and a somewhat powerful GPU, it's worth it though. There's also the 3d art engine someone made a while ago, but it hasn't had any work done in a...
If you're into slave management games, Free Cities Pregmod is a good one. You can get your slaves pregnant, they can give birth, and the children will grow and be able to get pregnant eventually as well.
I feel like they can work as long as the author knows what they're doing. One of my favorites is The Company, which is made with real porn images, although the author is slowly transitioning to drawn images which look better tbh.
If it's a VN type game, then Ren'py definitely, since it was made specifically for that purpose and it's very good at it. But if it's a game with actual gameplay, then something like Godot or Unity depending on the type of game.
These look very good! Congrats! Gotta be careful with the clipping though, in the first image the 2nd and 5th girls from left to right, and the MC, have their hands going through their clothes.