Part II and III is primarily Marty's arc though with him overcoming his brash nature of letting others rile him up which gets him into trouble.
I'd agree with you on 2 but with 3 I say it's primarily Doc. It's his love story, it's his character arc. All of the major things in the story revolve around him and while they both grow at the end, I'd say Doc grows the most.

that a movie about time travel was well written enough to be fun enough to capture the imaginations of kids and be fulfilling enough for sci-fi heads.
about original ideas as they are - I wonder if they would greenlight something like this today.

or not but i had an ole head tell me when he was in desert storm he he ran across some devices that were similar to the IPAD while unloading a truck.