Two suggestions: Get a large CompostTumbler... it's my favorite gardening tool. Look into possibly hanging your dehumidifier rather than supporting it from the floor to save valuable floor space.
Why are you going with such large pots? I may be wrong but I think the max amount of flowering plants is 24 for any grow in OR (You can only grow for 4 people total, right?), so that's 4 per light. Looks like you're running about 40W/square foot, so let's say you do four plants per light, that should give you a bit less than 30" for each pot diameter. So, either you go a little smaller and run a 45 gallon (27" diameter) or larger with a 65 gallon (32" diameter). Why the 400 gallon pots? seems very inefficient for your space... Are you just putting one plant in each of the 400 gals?
Also, should you need to refloor this in the future, check into rubber pond liner.