Players pay in the community's currency, Robux, which Roblox then converts to real cash via the Developer Exchange program. Of the 56 million total Roblox players, 1.7 million are creators. Each of them can technically earn up to $1.05 million per month.
Another way of thinking of monetizing a game is by selling add-ons. A great example of such a strategy is the massively popular The Sims series. After purchasing the standard game, players are offered many expansion packs to get even more fun out of the game. This model is also used a lot in mobile games.
It really depends on your strategy. Free games can draw 4 to 6 times as many users than even a $0.99 game. The question is, how effectively can you monetize on those customers once they get there? Also keep in mind that if you're going to use micro-transactions, you'll have a lot more to consider.
YouTube, in short, will not penalize you for uploading gameplay videos, except for a few exceptions: The video or description violates one of YouTube's Terms of Service, which you are required to follow (rules on abuse, hate speech, etc). You have copyrighted music playing.