I’ll mostly share tips regarding what you said, OK?
Quite a few programs still rely on files in ~/.config/. So if you feel like the options in a program are “missing”, give its config file a check. (To see hidden directories: Ctrl+H)
There’s another MS Paint alternative called Kolourpaint. I personally prefer it over Drawing; once you install it you’ll need to install quite a bit of stuff from the KDE environment, but I think that it’s worth.
The super key can be configured to your taste. For example mine brings up composing, so if I type Super+e+1 I get ɛ, Super+a+1 I get ɐ, so goes on. (I open the menu with Alt+F1, by the way.) As implied, as a further tip - if you need certain characters you can create custom keystrokes through a file called .XCompose.