That really is looking good Paul, and it's nice to get the extra water volume by using a square sump. The home-made rock really looks nice too.
I would put a valve on the end of the manifold. That way should you need to extend it, you can do so without shutting the system down. I just used a schedule 80 BV.
Also, what do you think about mounting the pump differently so you can lose the 90 elbow on the output? And I would put valves like the ones you used on the manifold before and after the pump, so that you can close them and take the pump offline for cleaning and repairs. It appears from the pictures that there's no way to close off the flow from the sump to remove the pump. Am I seeing that correctly, or have I missed something?