I see you have ball valves on the photos earlier on the drain lines...consider getting gate valves for just the main drain line as the fine adjustment is very nice compared to ball valves. Ball valves may still work, so it's just how easily you want to adjust.
Also, the 2 return lines, I would suggest adding ball valves for future maintenance. But this is optional. And I see 1 of your 2 return is T'ed off to the smaller tank, so you definitely want to add the ball valves to the main display after the check valve so you can regulate how much water is going into the DT and smaller tank. Just have the 1 ball valve between the DT and smaller tank will not regulate the flow well.
Pro-Tip: When you use clear check valves, always try to cover it with something so no light can get in there when full of water...algae will grow and it will stop the check valve from working. I put aluminum foil around my clear check valve, so I can always remove to see, but I always put it back on afterwards.
And for the return pipe that is T'ed off from the bigger tank to the smaller tank, I would add a union closer to the smaller tank, so you can remove that piping if needed in future.
Also, all of these long horizontal runs, you need to somehow support it with wall brackets or brackets mounted to the tank stand.
