1) there's a save folder that you can copy and paste inside the new version to keep your progress, but it's possible to result in some bugs so i recommend having a save in a safe spot like the stage select area
2) i think it's unlikely
3) i've thought about it, but maybe won't require items
4) it's been on my radar, but haven't written anything related to it yet
5) there's an enemy that i'm trying to fit to that concept so it's likely to happen!!
Thanks!! \(>v<)/