Good ideas.

One problem OCs have in this site but maybe it's something that all fan fictions share is that readers are more interested in canon chars. Canon chars are known values. OCs on the other hoof are a gamble. Who knows how good the story will be?

Add to that the fact that lots of folks are jaded, they see where others have failed or had problems with OCs and basically expect more of the same.

My view is that if I want to go pro, I should be capable of making my own chars. It's one of the fun parts of being a writer. To use the ability to create a world and interesting chars from scratch. In fan fiction, OCs however well or badly made are second class citizens.

A lot of times, I find writing fan fiction onerous. Too many constraints. I've heard that even in writing, you have to be careful with picking coat colors for ponies. I'm not just talking about black and red. A bad choice of colors could annoy readers. Of course they won't say anything but they will lean on the downvote button until it breaks. To be honest, I could care less about coat colors. I have to use them but since the coat color is not tied to personality or ability, any color is good for my chars.

Anyway, I wish you well on your story.