Whoa how did I miss this post? We're usually in the discord: https://discord.gg/rvy92VB . Glad you can be here @rhinox!! Let's answer your questions:
re: Health - player health is indicated by the amount of time spent flashing. The faster you're flashing the closer to death you are. No one flashes at max health, and everyone flashes the same at 1HP and (Max Health - 1) HP. Inbetween is a gradient.
re: Single Player - it's coming! I usually talk about stuff on my twitter or the discord. Single player is going to be like the original NES Legend of Zelda. You'll start with a few characters and items and you'll search a big overworld + dungeons for other characters/items to reequip at basecamps. New items/characters will open up different methods of traversal throughout the world. I'm planning on having random seeds to redistribute characters/items so that you can play it over and over again.
re: Wishes - this is a good list! I will be emphasizing player difference via the stat system, but I do love the idea of earth element stuff. Physicality is really one of my favorite things in the game, and I think a boulder type attack could both mimic and contrast the Book of Barriers really well.