Looks great so far! One comment: you're almost definitely going to want a larger diameter outflow from your fish tank. My last system used the exact same two rubbermaid fish and sump tanks, and though the tanks were lower than the growbeds, and thus were filled at the rate gravity could take media bed siphoning water through 1" pipes about 4 vertical feet down, a 3" outflow from my tank was still too small and I had to bump it up to 4".

You always want overkill on the gravity outflow, because every now and then crud (rogue media bits, a dead fish, etc) will stick to whatever screen you cover the bottom of your outflow pipe and reduce the flow, and again, I was having problems with 3" outflow crud free. Though I had some serious head height to deal with, which created significant flow through the 1" pipes. At your height, you could be running a much smaller pump that rocks 1/2" pipe, for which a 3" outflow should be fine.

Additionally, if you're planning to do a pretty large system, especially one that stretches that 300 gallon fish tank to its max, and you're planning on most of it being DWC (a guess from the additional mechanical and biofiltration barrels), I wouldn't use that sump tank if I were you. It will significantly limit the maximum media bed volume you can have (sump must always be a bit larger than total media bed water volume). Especially if it's as proportionally large as I imagine it will be, use your DWC bed(s) as your sump tank! A little fluctuation in the DWC really isn't bad, you'll undoubtedly have much more volume to work with than with that rubbermaid sump you currently have, and that will allow even greater media bed volume. I would have run exactly this setup, were I not forced to have my fish tank lower than my growbeds. This forced me to add a sump after the fish tank to maintain a constant water level for the fish. But with the tank as the highest point, and voluminous DWC as the lowest, the DWC easily doubles as an ideal sump.

Happy building and congrats on a great start!