Don, I can empathise with the windowsill dilemma, certainly in late winter and early spring with those first sowings! Eventually, an electrical supply to the glass house will keep all those module trays out of the house here.
Great project building your own greenhouse from scratch and means you can really taylor it exactly to your needs. Good luck with it.
I like to grow my toms etc. in the soil, mainly for reasons of health. Of course I can’t be certain, but feel that the plant must pull up nutrients from the soil in a way that it can’t from a pot, and this ‘goodness’ eventually ends up in your body. Something more intuitive than scientific!
Yes, here’s to a great new growing season for all. Tris