Yeah, actually I'm planning on making a "story mode" with levels that have a gradual difficulties (like you said wider gap first :D), for this "arcade" mode I'll stick to easy-hard option. For the switch button, I think you're right, it's a good idea to put switch buttons on the game setting menu, but first I should make a setting menu firsst I think. I'll working on that.
Thanks for your suggestion Peter! :D