Steve, I have to start almost everything (except beans, corn, squash) in the greenhouse or it is eaten by field mice. Especially greens. (And I have six cats and four terriers that work to remove the rodents). It would be so much easier if I could start them in the ground! Most brassicas are cold hardy where I live. The ground never freezes.
Yes, I start my potatoes from TPS, true potato seed (as opposed to 'seed' tubers) in the greenhouse. They are grown like tomato starts, only they are a lot more fragile at first.