I usually use 1 hand to move pots. I put together a 6L gravel pot... 2 hands baby!
There's a good argument for hempies vs. big DWC. A 23-gallon reservoir weighs almost 200 pounds, LMFAO. Of course, those don't tend to get moved on a regular basis, but one never knows. I can remember the very first time I ever ran one, trying to follow the general advice of changing reservoirs once per week. I was thinking I needed to keep the thing topped off and, well, young plants don't transpire a great deal of moisture per day. Took both the (then) spouse and I to pull/push it in to the bathroom and then dump it over the little lip into the shower. The next couple of weeks passed without a reservoir change, and then I thought to spend $1.98 on a little squeeze-bulb siphon pump at the hardware store to facilitate draining the reservoir in place (to smaller containers). Later, of course, the plant took care of emptying the reservoir.
In all my led lights, the fans blow out the sides.... this is where the ducting would have to run unless you change that. Your idea of collecting off the fan vents might be off.
Ah. You favor exhaling, but never inhaling, eh? Some folks would rather cool a fixture with air that is actually
cool.
Otherwise, why bother with either? If you only concern is the
quantity of air moving through the panel, you can simply swap in larger internal fans (assuming you feel the need in the firs place) and call it done, yes?
In my perfect world (ha ha ha), all grow spaces have two separate ventilation runs - one for the lighting, and one for the space in general. Carbon filter on the latter, of course.
(My world hasn't been in such a state for years
. But that's still my preference.)
. And that is the same face I made when he told me that. I know that Hempy isn't the same, but I don't see why we can't pull 4, unless of course You have poor lighting like me. 
