I would plumb the UV right into the system via a manifold.
I would have changed the gate valve
I would have reinforced the stand
id have NOT gotten the Clarisea, as awesome as it was, it really can decrease the system turnover through the sump. hopefully when they make a gen3 it'll be capable of 2000gph+
truthfully, id probably went a different route than Redsea, obviously not waterbox cause they screwed me over. but probably something more custom made, or even the Innovative Marine new big tank, it doesn't have center brace support but does have the eurobrace around it.
I have a little 50G AIO that I am keeping until we move next year and can then go larger again. I will definitely do a basement sump this next time.