1–Yes, you can use the marketplace downloads to learn how to do similar things, part of a stylized look will depend on your assets as well though.
2–Those student licenses of Autodesk programs can’t be used for commercial products, if you intend to sell your game you have to get a commercial license. Also, if you plan on getting other people to help, figure out a good fee to pay them rather than a royalty percentage, you can pay them from the royalties you make after the game makes money, but don’t do just a percentage take for people.
3–Blueprints are a way to setup gameplay, it’s a visual scripting tool.
4–Most things are a graphical difference, mobile does things the most different. For controllers, it supports the Xbox controller, but probably not anything else, you’d need to add support for specific controllers yourself if you want the game to support them. That’s a more complex programming type deal.
5–You can create levels just fine, if you want things to connect between them then you have to figure out how that data gets passed between them. Saving is entirely dependent on the game, since what information needs to be saved is going to be completely different between games. The process to figure that out would be like figuring out how to save information, then how to read information, and then how to apply that information.
6–I haven’t messed with audio at all
7–Of course, you can do anything completely different from level to level.