I may have missed this but what size is your UV? With the plumbing scheme you have, you will have to match the flow to the UV as you suggested. Have you considered putting the two canisters on separate loops? You are pulling water for three pumps in the existing diagram - this will need a pretty big pipe to handle the flow and prevent cavitation. What diameter pipe are you going to use? If you just had the two canisters they would share an intake but one could return to your spray bar and the other to the top of the tank. If you plumbed the UV into one of those lines I would gues the flow would be appropriate for killing algae & bugs. For flow, you could add a power head internal to the tank and save some $$ on electricity. When your plants grow in they can hide the power head pretty well. I am sensitive to the electric cost as Califonia has a sliding rate scale ( $0.28/kWhr). With three pumps at 140 watts each, our bill jumped 60% over last year!
I would also suggest moving the ferts to a post pump position so you don't feed the filter sludge before the plants. You will have happy bacteria but could cause slime to build up quickly in your filter.
Looks like fun though, I think I need to another project!