Morning Querteronion, your plants are looking great. As for soil KindSoil works great, and for your light height, being its your first grow, I believe I would go by what the manufacturer says, or read what Nebula says about Led light distances from your plant , also read what she says about using co2.
Your doing great for your first grow and all and we want to see you get thru your first grow without all the headaches, it's hard enough as it is for a first grow to make it all the way to harvesting nice buds.
After you get more experience, then you might want to try other ways.Read what Nebula says about Led heights and adding co2.
Adding silica or kelp helps tremendously with heat problems, they help lots of other things too.
I'm not knocking what Tyler says about his light heights and co2 ,it works for him, but I bet not many people grow their plants with their lights that low, anyway just trying to help you get to harvest, Good Luck.