Tok, if you want MESS to be as user-friendly as I think you do, I recommend you don't try to do this project all by yourself. You have a *lot* of computers and a lot of hardware to cover - Types of floppy disks, joysticks, paddles, everything. Many computers/consoles have system-specific input devices, i.e. those input devices aren't made for other systems, or work quite differently on other machines.
I also suggest that the text used in the added user-friendliness is put in a separate file, rather than in the MESS.EXE file. This will reduce the compile time, make the EXE smaller, and also make adding/editing the GUI text less troublesome.