Recurring & scheduled to-dos - although it was tempting, I decided to leave it out. First because it's against good productivity principles (the less you commit to specific dates, the better), second because calendar software works good enough for that.

About multiple fields per to-do - that's actually against one of the key principles - keep it simple, be minimalist. It keeps your to-do list focused, not overloaded with too much noise and secondary information.

Done button - you can use "Space" shortcut key for that.