On stages: Personally I think the best thing for tournaments to do is Remilia or Patchouli's stages only. There's plenty of stages that are "fine" as far as the background obscuring bullets, but the indoor stages also don't show weather effects, so you don't have, say, Scorching Sun making it hard to see.
Ultimately it can be decided between players, but imo Cirno, Sakuya, and Utsuho's stages are awful for visibility.