This is really driving me nuts:
If ctrl+opt+cmd+h will open a Note window, I should be able to the close window with the same ctrl+opt+cmd+h, too. But now it’s ctrl+opt+cmd+h, then opt+cmd+i (Hide Inspector) to close it, really awkward.
In this case, the shortcut you reference already has a secondary action that takes place when you use it again: it moves your keyboard focus over to the Notes field. This way you can simply hit the shortcut twice to start jotting down a note, or just once if it is already open to Notes. All of the Inspector navigation shortcuts work this way. They make it so you can add keywords, view snapshots and do a number of handy tasks without having to resort to the mouse.