If your seedlings are getting temps between 60 and 70 degrees, personally, I would not add extra heat. They need the extra heat for germination, but excessive heat will dry the soil too fast, as you experienced. Too much heat will cause fast plant growth, leggy plants, even with them under proper lighting.
They are concentrating on root development and will take off when ready
I rarely fertilize seedlings, unless it's something that must be kept in pots for many weeks, like some perennials.
Most things shouldn't need much, if any, if started at the proper time.
Tomato seedlings
Some have success with the peat pots, I have not. The clincher was a few years ago. Impatien seedlings in peat pots stalled out at about an inch and a half... the ones I had in plastic pots (same seed, same growing medium) were 3 inches and starting to bloom. I find it impossible to keep the moisture from being wicked to the pot without keeping the soil wet.... causing mold, fungus, over watering, etc. Better to water thoroughly and let top soil dry out between watering... they just did not work well, for me anyway. :/