Not a veteran, never finished a project, have messed with all the tools you're thinking about though pretty thoroughly. I just abandoned those projects.
If you want to make a renpy game using koikatsu to make the artwork you only need 1 person, yourself. It would progress a lot faster if you had another person to focus on making the artwork in koikatsu since you could write while the other guy makes the art but you can really do this yourself.
So long as you're sticking with the basics, making a normal vn without any non-standard features, ren'py is laughably easy, you don't need any programming experience that you cannot get by installing renpy and following it's tutorial which teaches you basically everything you need. For this kind of game you do not need a dedicated programmer, it's better to have the writer handle those parts unless you're doing something unorthodox.
You don't need a budget at all for this kind of project either.
Like others have said though, if you want to make a high quality product you will not make it with koikatsu artwork, you'll need real 3d software (daz3d is really perfect for this, it's why so many h game devs use it, it's almost purpose made for this) which involves manually setting up your environment, lighting and all that jazz. Then you gotta render it which takes time and gpu power.
These are all tougher to learn skills, the foundational basics of 3D art.
But if you want my advice, skip all that jazz, just make your project with koikatsu like you originally planned and don't be overly worried about the quality.
It's your first project, I think the main thing for you here shouldn't be to try to make it a smashing success, but to prove to yourself and others that you can do it.
Just keep the scale small, don't try to make a 10 hour long game. When you're finished with the first project and have gained good insight into how the development process goes, then you should try to figure out a way to make a better game.
Also, if you're making an nsfw game in a country where it's not legal, i've had to think about this stuff too. If you're gonna go this route, you'll have to do it for fun, make the game free, release it anonymously through a vpn you trust (recommend mullvad) on an account that was created through that vpn and so on (basic opsec) so there's nothing leading back to you for your government to track you down.
If you want to do this professionally, make a few free games and see if you can't figure out a path towards making a real hit of a free game, then when you've got your formula down you could gamble. Make a game you're sure will be a huge hit, complete the whole thing, move out of the country and release it, start a patreon or sell it or whatever. But like I said it's a gamble, you can lose and lose hard if you do smth like taht.