You've obviously put a lot of thought and work into your plans, but perhaps you're over-thinking things a little bit.
Wouldn't you be able to achieve exactly the same results, but only have to use a single sump/fuge and a single return with melev's plan F?
http://www.melevsreef.com/acrylics/sumps/f/sump_f.html
Aside from the complexity, the main issue I see with your plan is that you would have two tanks draining into your sump in the event of a power outage. The result is that you'd have to have a lot of empty "safety" space in your sump to absorb this water leaving you with precious little water volume in your sump unless it's very big.