I know you wanted to make her boss fight really hard because I know she's the goddess of the galaxy (or something like that). It's honestly really cool, but this just seems too much imo. Not because you can't survive her attacks, but because your party will always need to be at its best to be safe, and that draws battle out for too long that you'll run out of items eventually. Her Galaxy Blast move is the main reason of this. If this is what you'll have to deal in Normal Mode, I don't wanna imagine how absurdly hard this might be in Hard Mode.
Also, I've seen that from the video you linked (super buffed rosalina after the beta test), she seems easier there. She doesn't counter Galaxy Blast which already makes this fight 50% easier and do-able.
By the way, I think I've found the reason why she does Black Hole-> Galaxy Storm. She only does that when you attack her when you're past your 3rd party move (which will only be possible if you have an item that grants haste), isn't she? If that's so, then I could come up with another strategy.
I like hard challenges, but there's a fine line between challenging and unfair.