I'm by all means no expert but the biggest flaw I see is bypass. With your tanks emptying into the live water barrel, there's a good chance that your pump will just direct that water back to your tank. I think it would be a better idea to have the incoming water from your tank go into your wet/dry filter. I probably would get rid of your live water tank and canister. Just build a bigger wet/dry and still use your ro/di tank for top offs. Your wet/dry will have all your filtering media. The hardest part is going to be balancing all your waterflow so that output is the same as the incoming water. This will become worse whenever your filter media gets clogged from gunk thus decreasing water flow.