These are all questions which the person issuing the orthoses should be answering for you (and make sure you have these answers before you commit to proceeding). However I personally would be wary of anyone who uses the awful term 'overpronation' like a diagnosis. I am also of the personal belief that not all professions/professionals are equal when it comes to their understanding of when orthoses are and are not appropriate. I would generally advocate seeing a Podiatrist in conjunction with a Physiotherapist for these sorts of issues so they can work together to get things back on track for you.
Whatever is decided upon I wish you all the best for recovery.
"Can someone please explain what Mid to moderate overpronator means"
It means absolutely nothing. It is ambiguous, undefinable and utterly useless when considering either dynamic foot mechanics, correlation with lower extremity injury or running shoe selection. Yet running shoe companies and running magazines continue to use/print it.... Go figure.