This year, I am mixing only coconut coir and perlite as a seed starting mix. The mix consists of equal parts of both. I am not adding vermiculite to the mis this years because it doesn't seem to add any benefits to the mix.
A simple Mr. Heater Big Buddy propane heater is keeping the 144 s.f. greenhouse in the 50 on medium and in the 60s on high, even on the coldest nights when temps dip into the 20s.
I expect the seeds to sprout in a week or two, then grow for two months before being set out into raised beds by late March or early April.