Blue Dream Auto - Super Soil/LEDs

This is my first ever grow and I'm starting off with two of these Blue Dream autoflowers from Farmer's Lab (I've got some more seeds on the way and I'll probably plant two more alongside these, also autos, in another diary). I'm pretty limited for space as I'm growing in a closet, and I can really only use half the closet. The tent is 2x2x4 ft. which is just enough room to fit four 3 gallon fabric pots with some wiggle room. I've got a carbon filter jammed into the back upper corner ducting out the top to a 4" exhaust fan that is mounted on a shelf above the tent. Air intake comes through a single inlet at the bottom which is ducted in from a booster fan with a piece of furnace filter affixed to catch all the dust and cat hair from the room. I've got two circulation fans, one fixed on the heatsync of the light and another oscillating back and forth over the plants from above (mounted on one of the tent poles). My light is a single QB288 V2 board from HLG (built from the QB135W kit) and running at approximately 130W, 18 hours a day at 28" (once they have a few strong leaves I'll gradually lower this to around 18" if the plants take well to it). I planted these last Tuesday directly in the soil to germinate and saw the first sprout up Saturday, the second Monday. They look healthy and happy, I haven't watered again since the initial soil conditioning, I've just been misting the top layers of soil to keep things moist, my hygrometer indicates that the soil is still very moist a few inches down, the pots are weighty and I don't want to jump the gun on over-watering these babies. My soil is Dark Matter from Destiny, which I've heard good things about. Nothing but straight up RO water (6.75 pH and 300 ppm) from the store right now and at least for the first week or two, I'm not entirely sure what will come next yet because I certainly don't want to burn the plants with nutrients, they are autos after all. I might consider lightly foliage feeding them once a week through veg, some occasional water conditioning and doing a top dress of some kind as I move into flowering - more research is required and I'm very open to suggestions. I'll be starting LST as soon as I can and I'll likely start to SCROG when they hit about 12ish inches/3.5 weeks since avoiding stretch and capitalizing on bud points is going to be really important in this short little tent. Update: On advice from a friend who has more experience than me, I'm trying to raise the humidity in the tent closer to 70% for the first week or so to encourage strong root development early on. I'm thinking I might invest in a humidity controller and some kind of ultrasonic fogger in the future but for now I've turned off the intake booster fan and I've got a damp towel hanging in a bowl of water with the oscillating circulation fan fixed on the towel. I'm seeing about 8-10% higher R.H. in the tent right now with the lights on, tomorrow I'll see how this modification fares during the dark phase. I've also shifted around the pots so that there's a little more space between the pots and the air intake - I think that when I introduce two more pots to the room I'll also introduce a Y-joint in my ducting so that air flows in on both sides of the tent to mediate the effects of more air blowing directly into the side of one of the fabric pots (I was observing faster evaporation in the pot closest to the inlet). I've also lowered the light somewhat the 22" from the babies, I'll be monitoring closely to ensure this doesn't cause any problems.