Hope you don't mind all these questions. It's cool to be able to bounce ideas off each other especially because of the similarities of our grows.
I use a 27gal HDX yellow lid style tote that I got from Costco for like $5 on sale. It fits about 22 gal almost to the brim. I fill it to about a little above half too, 18 gal or so. I have an aquarium filter hanging on the rim and cut a piece off the lid to fit around it. Then lean that piece of lid against the pump to cover the waterfall as much as I can. No funk issues so far. I would like to move the aquarium filter inside the tote though so I can seal it up better and not have to fill the tote up so far to prime the pump. Once it gets going I can let it get as low as 4 inches to the bottom before it loses its prime and stops pumping. I've only seen the hanging kind of filter or bio-wheel filters. Thinking of attaching it to the wall somehow but there are no screw bracket holes or anything. Maybe some sorta water resistant mounting tape or Velcro.
Good idea for the quick waterfall. I had an extra cheap walmart pump I found last night so I tossed a couple airstones (came from the system buckets) in there to get some more aeration. Thinking of using a smaller res tote, because I may need two in the near future