I'll make the movie start off with shots of different planets and their people, leading to the scene in the manga where Galaxia overhears of the Galaxy cauldron (and Wiseman cameo!).
Then I'd make the movie based around fight sequences. I'd have lots of blues and golds in the palette and the girls would look more mature.
1. Show us some decent battle between Galaxia and outers (well a recording of it from their castles). Dont keep it as just the second of their deaths. Maybe also expand (even if just a little) on castles in general if possible
2. Make Starlights deaths a little more meaningful. Make them go down in a fight.
3. Show us more action for Asteroid Senshi. I would LOVE individual attacks for each and maybe even transformations?? I know im asking for too much
Obviously "give us a meatier wedding" should be athing but since everyone is asking for this i'll keep my ideas as above