Ph should be like 5.5-7, but 7 is a borderline, try to not let it go any higher. The seeds won't just instantly die if it will be like 7.5 of course but that might cause them feel stressed and the genetic itself can bring you some surprises later on like early flowering or any crappy stuff
Hm, well I guess that depends on how much heat you need. For me just the common heatfan works (on the lowest power setup), yes its a little noisy though. But it's compact and works from a common socket
I would say the roots do not feel free, perhaps changing the pot for the one that allows tips of the roots to come out, the plant will drop off the excessive part, or just a bigger pt. But yea, Ph might also be the case