No idea how it works. I just packaged it.
Last time I used WinUAE was about 10 years ago. I vaguely remember I need to supply it a Kickstart image.
The default GTK+ interface is completely borked. I hope ArnimS code will fix that.
I'm fine with writing GTK+ code, so the interface will improve. It's ~2h. of work so far. Give me some time.