I'm shocked, don't know what to say! The C64U is getting native mouse support in the next firmware update and this will get a lot of people even more hooked, I think :3.
Talking about control, I might opt to use an emulator for the map maker though, because even after so many years, using the cursor keys extensively for hours on end on the Commodore gives me knots in my fingers. On a PC keyboard I can just relax while making maps.
Thinking about starting off with something simple to get accustomed, like perhaps remaking maps that I know from perhaps Wolfenstein or Catacomb Abyss, once I have a way to test them and get a good feeling for the dimensions of when I draw walls and rooms, and what visually feels okay to do and what not. Like, attempting to make diagonal walls, how "wrong" that looks, and so on.
Thank you for all that hard work you put into this! Castles or Planets, anything goes. :3
PS: Ich know this is already absurd asking, I guess but if you support multi SIDs you could have stereo and waking monsters/robots could make sounds just like in other such games, or when they spot you, giving you the opportunity to know which direction that noise came from.