You're allowed to use any region of game you want, although getting a JP game to work on a US gamecube is a lot harder than on Wii and I think needs hardware manip. If you're gonna use a different region's game, I would definitely recommend using a Wii.

If you mean literally putting a switch in your console, I know of people who have done that but not on the SMS leaderboards. I don't think it would be illegal since it doesn't alter gameplay but you might have to ask a mod to make sure. As for using free loader or an alternative I know that that's fine as I do it myself.

ya sure