Cinnamon is a super simple DE for simple people. I don’t mean this as an insult, some people just never even think to customize their computer and are scared by settings and options. Just use KDE if it has features you like, you clearly sound like you’re up for the change.

1. They have an experimental Wayland session already. It mostly works except for some pretty important stuff…I also haven’t seen development on it for a long while.
2. I think this is almost a 100% no.
3. I tried to implement that myself. Making them shorter than the screen is easy. Making them appear above the edge of the screen is hard, but not impossible - the code is in JavaScript and the logic is kind of disjoint across multiple files and stuff depends on panels being at the edge of the screen - I didn’t do it in the end because it was too much effort for something I didn’t want that much.