Sounds like you are on your way. That combo will help tremendously. You may be pushing things a little with 20+ in a tent set up but you could always cull a few to make room.defeyter said:
I have them on a heating pad, and the soil is around 80 degree F range indeed. I also run a humidifier with warm mist, bringing the temp to around 80F as well.
I just ordered a 400W HPS/MH combo which I can hook up to the air exchanger to suck out the heat. The MH bulb initially has 36,000 lumens, and the HPS bulb has 55,000 lumens. For flowering, that makes a big difference.