Admirable, but artwork and fetishes aside, what kind of game do you want to make? Some engines are better than others for certain kinds of games, so you need to figure out what kind of game you want to make before you start making those other decisions.
Just remember you're making a game, first and foremost. If your game is fun to play, then it's fun to play. It doesn't matter how good your artwork is, or how many sex scenes there are, or how many fetishes you cater to. If you build all that on top of a game that's not fun, then it won't be fun, full stop.
I recommend not looking at current adult games for direction. Look at indie games as a whole. Are you making an RPG? What makes a for a good RPG? Visual novel? Interactive fiction? Look at the best and most critically acclaimed examples in these genres whether they are pornographic or not. (Usually not.) Use that as your benchmark for what makes a good game, then pursue that goal. The sex, porn, fetishes, etc... all that is secondary when you're making an adult game, and I think most adult game devs don't realize this, hence why most current adult games are a poor example.
Aim for the stars, but remember you're not going to even come remotely close to hitting them on your first try. Hell, most attempts at game development never even get off the ground, so if you have the wherewithal to see it through to completion that alone will be cause for celebration, even when it's terrible. (And it will probably be terrible.) Your next attempt will be a little better. Your third attempt better still. Just keep your sights high. It's easy in this area of game development to just end up shooting to satisfy the lowest common denominator. Half-ass some kind of GUI. Maybe some asset flip puzzle game. Add a bunch of sexy images as a "reward" for completing the boring puzzles. Put it on Patreon and pray the money starts rolling in. It probably never will since you will just be another one in a sea of other "developers" trying to cash in on content starved horny gamer's baser instincts. If that's what you want, fine. Maybe you're different though. Maybe you want to build erotic games that are actually enjoyable to play. That's a far nobler path to be on, I think.