if you double up on the high velocity fans for your scrubber/exhaust, that would be 100x better than just using 1 high velocity fan and a booster fan. the booster wont have enough "balls" to move any air, and will just inhibit your high velocity's fan speed a bit (the blades may be spinning, but it puts a small amount of drag on the other fans output. either double up on the h/o fans and put 2x speed controllers on them and dial them in together correctly, or jump up to a larger h/o fan, add a speed controller and dial it in (you may not even need a speed controller with the larger fan. this is all dependent on how long your exhaust ducting is and what size your carbon scrubber is. too much air flow can make the scrubber worthless (too much or not enough air flow).
I use fox farm ocean forest soil (amended with 1 cup powdered dolomite lime, and 1/3rd bag of chunky perlite per bag of OF soil. ive been using this for 4+ years and I doubt ill ever change whats been working. I don't use any ferts until week 6 in veg. Ive also been using technaflora ferts. its something I was given when I 1st started growing, and well once again whay change something that's been working.