Thank! I'm surprised the water has given so many people trouble, as I have a fairly modest system and while it does cause a little slowdown, it's very minor. These are the hazards of working RPGMaker MV though.
All of the custom art assets are used in the game, though I have left a bunch of the stock stuff in out of laziness. May finally strip that out of the patched version, but it wouldn't make much difference size-wise. There may technically be a few sections on the sprite sheets that don't get used, but that's because I wanted to err on the side of giving myself the option to use them if needed. Also RPGMaker is weird in the way it uses sprites so I have to fill a bunch of slots JUST IN CASE they get called, even though in theory they shouldn't.