I've been working on "small" stuff like the functionality of menus etc. but now attempting to tackle an important part of the UI design which is the main screen shown when playing the game.
Two usual ways to provide information is either display it all the time or preserve a space for it to display when something happens, or create a command to display some information. I think there are endless possibilities to weigh between easy access to information vs. displaying too much information at once. Also, everything you decide to display will take some space away from the game world area and increase the requirements for pixel resolution of the program.
Up to this day I have had some kind of vague idea how and what to display, but foolishly delayed the complete design in a thought that it will be decided when the RPG system is ready. It's of course nice to know what stats are displayed etc. but it doesn't really have a lot to do with the way you display things.