Disclaimer: I am not trying to discourage you in any way, shape, or form. I am simply just giving my opinion on this topic.
I would love to see a game like this!
But you have to first make sure that you are capable of making such a game like @SuperZebe1 said.
Scripting the platformer movement would take a lot of time. And the level design would also be hard to make. Especially with one person working on this. If you’re a beginner then I would just probably recommend abandoning this project and make a more simpler game to be completely honest. That way you can gain more scripting experience and knowledge and start this project again once you’re better.
Yes, but not in concurrent players though. Many great games on roblox are highly underrated. Take robot 64 for example, the game usually has about 500 concurrent players. But the game has gained a lot of respect from the Roblox community, and it hasn’t died off. In short I’m saying that if you did complete this project you would probably gain a lot of respect, and your game would probably stick around a lot and not end up dying off.
You could use a platformer character controller but the thing is, the character controller will probably not have the specific moveset you want. For example, it will probably not have the triple jump or roll.
@EgoMoose made a great open-sourced platformer character controller here.
Probably what you had said previously. You could just sell the in-game currency (not the collectibles that unlock the different areas. I’m talking about the tix)
Once again, this is all just my personal opinion, if you feel that you are capable of doing this project then do it.
Good luck!
Hope this helps!