I was a music ed major a long, long time ago and will try to add a couple things from that perspective. On your question about what to take in HS, take as much music as he can fit in without making academics suffer. Marching band and symphonic/concert band, jazz band, etc. If offered, consider music theory too.
Get experience playing but that doesn’t have to be all through classes. For example, my HS son now plays in the combo band for the showchoir, so gets some jazz/rock experience that way even though not in jazz band. He also played in the pit orchestra for the spring musical. And get private percussion lessons if you can afford it. Colleges will want percussionists to be pretty versatile on the instruments they play (snare, tympani, marimba, etc.).
On schools I can tell you NAU is a nice place and does meet the type of atmosphere you mentioned (at least years ago, but from what i’ve heard it is still similar now). I went to the University of Arizona but interacted a lot with NAU through the band fraternity/sorority system. Very laid back school but lots of opportunity. Of course I think UofA is pretty good too, but definitely more of a big-school atmosphere. We now live near Otterbein and my kids have had student teachers from there, always with positive feedback.
I think if you are looking for a less high-pressure place, most state schools would fit that bill except for some of the really big names (Michigan, etc.). But you will find competitive people everywhere so experiences may vary. I haven’t seen the movie you mentioned so can’t speak to that, but I thought Drumline was pretty silly from a college band experience perspective. I enjoyed the band performances, but found the plot to be very unrepresentative of the college experience. Maybe thing are different for the types of colleges represented, but mostly I think it was a movie taking artistic license and wouldn’t put much stock in it. I assume the same could be said for the movie you mentioned.