I am surprised that you can still buy Vermiculite!!!! It has been off the market here for years, when it was deemed to contain asbestos. I work at a HD--and we have not sold it for 5 years or more......
I do not do so many seeds that I need to worry about a roll of Seran Wrap. Usually, I don't cover my seedlings at all.
I also do not have any heat mats---but I do put my seeded cell packs on the very lowest shelf on my light rack, which sits right above a floor heat vent. So--I hope some of the heat gets near the seed trays.
I have a very small seed rack set-up and only use 3' lights on 2 shelves. It is by a S. facing window in my bedroom.
That is all I have--and, need.