You have many good ideas! Older directors who have stayed with one district for most of their careers have a big advantage over young directors. I had the advantage of band not being required of all beginning students. I would visit with 5th graders and show them all the instruments and give them the opportunity to tryout every instrument I could disinfect. I would keep scores 1-5 on every instrument so I could help them choose what I thought they would be successful playing. A few students would not choose band so I seldom had the "I want to quit" attitude with those that elected to take band. In my last few years I had many classes of 100% retention from 6th to 12 grade.
Success of the older classes also helps retention. (A couple of Honor Bands were helpful.)