1/a. I only managed to calibrate it once when the two directions weren't mixed up, but it got messed up again when I started the program the third time.
1/b. It wasn't an axis being reversed (up is down, down is up), it was the two changed up (up is left, down is right). So there's no way to fix it on Linux at the moment.
1/c. I'll check out wejoy, thanks.
End result: I'm using my laptop instead, booting win10. Having loads of fun. I'm still terrible at it but in my defense I'm starting from Acro with high rates so it will take a while. Sometimes it clicks and I make a bit of progress and it feels awesome. I probably won't even try flying my quad for a few more weeks before I get the hang of the controls.