Your post is timely, as I have been "working" the space in my fish room in my mind over the last 24 hours planning things out for my next big build (240-300 g setup). I would prefer to do gravity feed from salt water mixing reservoir into sump and by gravity from sump into main house drain line (this is all going to be on the lower level of the house with access to that behind the scenes), but space/configuration in the fish room may not permit that with room to walk around and access things easily. In that case, plumbing up with pump transfers as you have done will be required (which will let me put different drums in different areas in the space that is available).
I see the answer to the first question I had, which is where you got the drums (usplastic.com)
Next question: where'd you get that sump? It looks great!
(By the way, are you using the fresh water reservoir to feed topoff and if so are you doing it automatically or just manually? I didn't see any apparatus for auto topoff.)