What I came up so far are the following rules for my playthrough (Update 3): I never played this game, but I watched a playthrough on youtube and it was great but seemed way too easy, and now I searched through the internet for things like 'badges that are too broken and overpowered', etc.
What kinds of limitations would you advise to try? I recently wanted to challenge myself in the first Paper Mario (Nintendo 64), so that the game is harder to beat, even though it would be my first time playing it.