I think a lot of your answers are in the Soundtrack guidelines. these guidelines apply to a few of your examples, like Galavant or La La Land
according to them, works from TV series should be all grouped under one Soundtrack work for the whole show
for example, The Goof Off here is under the big soundtrack work My Little Pony: Friendship is Magic, even though there’s multiple songs in this particular episode of the show. the episode name should go in the disambiguation too
I will also note that (at least to my knowledge) only songs written for the movie or show should go under the soundtrack work, so a soundtrack like Baby Driver or Pulp Fiction (both of which mostly use existing recordings as their soundtrack) would be missing most of the songs that appear in the movie (neither has a soundtrack work as of yet). I know there has been a few discussions about changing this, like here
for live shows with performances, I’m not sure how best to handle these, and I don’t really have much input here either. a release might make sense, but as far as I know there’s no precedent for such a release
YouTube videos can and should be added as releases, so at worst, these can likely be added (official channels are preferred, but unofficial/bootleg releases should be fine if there’s not an official release)