I spray them several times with a mist in the morning and at night as their source of water. Is this ok?

Don't mist at night unless the lights are on. Never have wet plants duning the dark period if you can avoid it. Also, you don't want to overwater, but misting should't be their only source of water.

What medium are you using? Doesn't really matter, so long as the soil is constantly damp, not wet. Misting is fine for seedlings.