For full screen in WinUAE, you have to select filter (try all of them) and then use it to resize the screen.
F12 should bring disk change option even in full screen.
You can use WinUAE to create empty floppy, but make sure that you select DD floppy, which is amiga's 770KB.
Most of amiga games were not make to work as hard disk games, but thanks to WHDLoad, you can install those games to hard disk.
The easiest way to setup amiga desktop is to use
Amiga in a Box (AIAB). After you properly install it, you have to get
WHDLoad, user version. From the same page you have to get WHDLoad installer for ITFD.
I have somewhere installed version of this game, just have to find it.