Something you have to be clear about.

The video game market is an ultra-saturated market.
If you want to make money, it's not enough to create a game, you must also invest in advertising and create a community.
It's not impossible, but it's not easy and it's not quick either. Unless you have a stroke of luck. This also applies to VNs, even NSFW ones.
If you expect to create your first VN without having any prior experience, chances are you won't make any money, or even cover the costs of producing the VN.

The questions you ask are not a good sign. Don't get me wrong, it's okay to want to learn and ask questions. The problem is that these types of questions, to be answered correctly, require precise information, usually with a market study.
In a forum like this, what is usually obtained is more anecdotal data and therefore, it is less reliable.

It's okay if you consider them general tips and want to do something for fun.
But considering this information as reliable, in a business model, where you are going to invest and expect to make profits, is a bad sign.

Tools are like shoes, each one has certain advantages and disadvantages that depend a lot on each person.
For example, blender is possibly the most powerful tool of those you mention, but at the same time it is more complex, it requires you to dedicate time to master it.
DAZ is an option that requires less time, but is more limited.
If you want good results in a short time, DAZ is a good alternative. But it is difficult to recommend something without knowing your knowledge and what you are going to do.

For example, you can achieve wonders with UE5, but again, you need to invest a lot of time in learning to master it, in addition to learning how to program.
I don't know if you are programmer, artist, writer, etc. So I'm not sure which tool could be more useful, nor do I know if your plan is to spend a year learning to master the tools before creating your game, or if what you want is something that lets you create the game in two clicks. such a way to fully dedicate yourself to the story and graphics.

Before thinking about investing in optimal hardware to create content with DAZ, I would recommend that you create something simple so that you gain experience, know the market and start making a name for yourself, that way, it will be natural for you to know if it is really worth it to you. or not, invest in that hardware.

It's not impossible to make money or even make a living from it, but it's complicated, it takes effort and you're going to be competing against 100 other people who are making their own NSFW VNs and trying to sell them and that's the reality.

1. Is that a trick question? Let me rephrase that. Are games paying well? Yes and no. Some do. Most do not. Think about actors and writers as a comparision. For every known actor and writer that "made it", there are a large number of unknown and struggling artists.

2. Nieche. If you compete against mainstream you compete against mainstream. And those developers know what they are doing and have more expierence. Just sort the aduld vn by ratings or top selling and see for yourself what is popular. It aint't hard.

Steam has adult content. Just look what there is availablt. I am not discussing adult kinks in public forum. If you wanna do a kink that is not there, it probably is against the respective tos. And if you see it there plenty often, it should be obvious, that it is allowed on the respective platform.

Ratings are not really to be trusted for any controversial things. There is always people not liking what you do. The best advice is, not to surprise people. Do not make a vn that turns out to be gay, but making players believe it were straight.

3. Whatever you can make. Draw on paper and scan it, if it looks good. Players care not for that. They care for eye candy and story and sometimes even game play. If you can't write an engaging story, nor create stuff that is nice to look at, nor entertaining, it does not matter if your "tech" was good.

4. Before you upgrade your hardware, try out what you want to do. Do not fuss over details like that. Bad hardware will not be the hurdle to make a vn. Those run on a toaster.

5. One does not set out to be a famous and successful game developer just like that. You will very likely fail. Maybe start it as a hobby. What I said about the actors and writers. 

In terms of visual novels I'd recommend going out and getting a root first.