Mini splits are more efficient, but you need multiple units for large spaces. Central HVAC systems w/ air handlers are more expensive to install, less efficient, but can move lots of air quickly.
They do look a little burned but also could be nutrient lockout. Maybe your PH might be off? The buds should fatten up more. Most of the time they swell up the last few weeks before harvest.
I've noticed temps in the 70's vs 80's creates a more quality product. Keep the plants watered and happy consistently, and don't rush anything. (harvest time, drying time, curing time)
I would recommend using the cooltube, that way you can transfer the heat into the room. It would help raise the temp in the room the box is in, and help prevent condensation on the grow box as well.
Very Nice Space! Looks like some sort of 1st floor basement?
Regarding the smell, I would maybe air seal the ceiling first by installing a layer of drywall on those joists & maybe even insulation or foam. A bead of caulking around all air gaps. The more sealed you can get it the better...
I usually only have just one fan running (6" inline exhaust) and I have enough air movement. I only turn on my small canopy fan when temps are getting into the 80's, to cool it down a couple degrees.
Vapor Pressure Deficit. So you would want to be in the orange on that graph for optimal growth. Thats the sweet spot. Although when growing cannabis you don't want your humidity to be above 60% unless you want moldy buds.