. I have all those things but, hope my plants are started by May. Mostly use barn gold here 
Things that do best for started plants -- tomato, peppers, eggplant, etc. Most other veggies are direct down here. Garden isn't ready for that part, maybe 2 weeks out. Usually I'm further ahead but, crazy weather has held me up. It'll be fine. I'm blessed with a decent grow season here.
I have never had a tomato come back from the roots. If the top breaks off, you may be able to get new roots growing from the top part but the original roots will die and they will not come back as a new plant.
I once had a population that was pretty cold tolerant, but that wasn't my goal so the seeds got mixed in with the rest when I was finished. I wish now that I had kept them separate. I was testing to see if they would flower earlier, and they never did. Four years in a row they were planted early, the last time in February in the snow. Protected, of course (wall-o-water) but the last year they did just fine as long as snow was kept directly off the leaves.
(vicarious enjoyment 
