1. Depends on the 3D game.
There is a massive difference between a 3D game where you walk around levels, and a 3D game where you have satisfying shooter gameplay, a 3D game where you have character customization & rendered, physics based sex scenes, vs. pre-rendered sex scenes and no customization.
2. If what you mean by 3D game is Daz3D renders, then you're going to have to consider that there's going to be a whole set of costs you may not anticipate. Depending on the specifications of your game (story, setting, characters, outfits, etc.), assets would have to be bought (if not in posession) and especially if you want fast work, a dev may or may not need to buy a second computer to render scenes if you want them to be very high quality.
Rendering a small scene (character, background, light effect) can take as a little as 1-5 min. Easily done.
Rendering a big scene, (3-4 forground characters, large prop background, background characters, vfx effects, multiple light sources etc.) can multiply that by a lot. Then you can easily end up at 15-25 min minimum, up to literally hours.
So if you plan on a small story in a family apartment - that's something most Daz3D devs can render relatively quickly. Large Fantasy or Sci-Fi world sets? Takes a lot longer and usually also involves some trickery.
3. You're going to have to deal with devs from all kinds of varying levels. A good idea is to pick a game or scenes from an existing game and use them as reference of what you want. That way, you can indicate the kind of game & type of quality you want.
4. If you keep the story secret, you're probably more likely to get people who want the money and get the job done some way, instead of devs that feel like your game is up their alley and something they're motivated to do.
Once you agree on standards & make a contract with a dev - you're both comitted to that. If the dev just does the minimum necessary to meet the expectations to get the payout...there's nothing you can do about that. That's why you should look for someone who's enthusiastic about your story.
5. Unless you're a professional writer, I'd be cautious about creating scripts and sticking to them. It's easy to imagine a story and write some kind of rough script, but implementation rarely survives it, especially if you don't have experience in visual storytelling (which is different from purely narrative storytelling). Stuff that seems to work on paper, or that you imagine would be neat, may fall apart when implemented in a game or scene.
If you find a skilled dev, you're usually better served with an overarching experience and certain themes & plot points you're interested in, that the dev than aims to implement, rather than a straight sticking-to-the-script dev. Because the latter may just really do that. Stick to the script, whether it works or not, and then shrug and call it your fault. (Which it is, but that's not helping you because you don't get the thing you want)
So you should be a lot more specific about the kind of experience your game should be (game mechanics, core gameplay loop, story type, fetishes) to attract people that WANT to make your game, and you should give information about the quality and scope of the game, because you can have anything from a 2-5k intial cost, to 50-100k.
Also, keep in mind that since the game's so closely tied to your story and what you want, any game dev would be limited in patreon & other final payments by how good your work can be implemented. So there's the danger of getting a dev that charges high initial cost, because they know they won't be able to get any long-term revenue from it, because there just never will be that kind of patreon support.
