I like your thought process on tip of what not to do. I do not read many OC fics becasue of the reasons you stated. There can be more canon there than one with all band members! I will admit that I MarySued myself into one of my chapters, but not that anyone else would have noticed becasue I did it through the main character.
I am really glad you also wrote about plot twist change ups. Did I mention that i hate canon? ^0^