You have enough room......you won't have to add any height. No central res; each rubbermaid tub IS your res....one for each set of plants. You move those little tables, buy a couple rubbermaids that are big enough (but not too big) to fit the lids of your plants...same dimensions or slightly smaller. (Tip: You might even get take a bigger rubbermaid like the rubbermaid you have and cut the top of it to fit your smaller lid....you may need some extra support for the lid however....) You will need to be able to drill (or punch) 2 holes near the top of the rubbermaid to put add 2 1/4 inch airlines and two airpumps that will power at least a 30-60 gallon fishtank and four 10 inch airstones ((2 in each rez) I'll dig up a link to the kind I use to try and get some photos.

Fill tubs 1/2 way with your nute solution....add 2 10 inch airstones per bucket (hot gluing them to bottom helps) Usually 30-60 gal air pumps have two outlets in each pump and will power 2 airstones. Hang plants accross top letting bottom of roots dangle in the water. You should have the lower 1/2 of your roots in the water. (consider this when buying your rubbermaid....and that the roots WILL grow more.)

Now wait....I KNOW what you are thinking but its not the same as your deal. This is pretty much my setup and my plants generally work out ok right? Trust me here. The two airstones will circulate your mix and add plenty of O2 to the roots and help circulate both to those millions of roots. Your plants will draw up the water and the nutes as needed from the roots in the water. Thats called a deep water culture setup.

You'd be adding nutes and water directly from the top. Check and add water or nutes/adjust ph etc as often as necessary. No more ebb and flow.....plants stay this way 24/7. The key is enough airstones/oxygen, room for the roots, and keeping careful track of the plants' intake.