Questions on mode advertising from Youtubers

So, I apologize in advance for the fact that there is a chance that I put the question on the wrong topic. I’m just a little new here so I did not understand on what topic to put the question.

Explanation of the situation
Okay, let’s get to the question. When I analyzed the options for advertising modes, I realized that most of the modes have a bunch of clips on YouTube, while advertising this mode is not in Robloks. And I came to the conclusion to get a good online should do his ad on YouTube (correct me if this is not true in the comments). So here, and here I have a question.

Let’s imagine this situation. For example, I have a mode in Roblox, it is anime mode, a mixture of simulator and tycoon. And then I have a question.
1. Which YouTubers, and in what language is the most profitable and cheapest to buy advertising?
2. How much will it cost approximately? Give examples of how much it would cost if I want. a) 10 online. b) 100 online and c) 1000 online.
3. How do I get in touch with these YouTubers?
4. Give me an example of how you bought ads from them, how much you spent on them, and what kind of online you got, and tell me if it was profitable for you.

Other issues
I also have a couple more questions, for those people who know to advertise pretty well. Can you please tell me how some of the modes linked below are gaining just a mad online, several thousand people? Do they just throw a lot of money at YouTubers? Or, do they use other ways?
Here are the links:

Other issues 2
Here’s another question, I have enough skills to write modes in which about a thousand online, and I even have good money. If what I’m talking about is dollars. The question is, is it worth doing? That is, as you can see these modes are just copies of another mode, but they have a good online. I can write too, a similar mode. But here’s the question, what about the ads? And is it worth it to do such modes now? That is, I’m currently pondering between such modes, which are the last on the list of games. And between anime simulator which is also popular. Yes, although it will take more time for Anime, for me personally it’s more interesting than a copy of another mode. Hope for an answer)