What ever you do, be realistic !!!
This market is hard to start in, but if you are in for the long haul, it can be sucsesfull .
In this bussiness, luck, favourable conditions and lots of work, do more than reading all the books you can .

Wishing you all the best !!! ( been there, done that .)

kale, arugula, carrots, radishes, lettuce (cold hardy types), leeks (must be started in spring but do incredibly well in unheated hoop houses over winter), spinach, raddichio, parsnips. pretty much anything that can be gorwn in early to mid spring will do well over winter.

The rub for you is everything must be started in August except the fast leafy greens such as arugula and lettuce and radishes or you will not get a harvest until April.

Also know that despite what Mr Coleman says things do not grow well or fast in the Norther US without supplemental heat and light. I have been doing season extension in WC Ohio for the past 12 years and have rarely had a winter when we could harvest Mid Jan through Late Feb because the crops go dormant. i have talked to other growers who have put heaters in their hoop houses and have fixed that problem (but heat costs money so we don't do it and just don't sell such things in winter but do sell onions, garlic winter squash and other things from the root cellar)

When "growing" in the winter it's not growth that you're looking for, it's harvest. Growth stops in mid December here and doesn't start again until almost mid February. There are a lot of plants you can grow in an unheated greenhouse to harvest during that time.

I learned over the past winter that warmth makes a big difference. I thought this was going to be all about light and day length over the winter. I wouldn't add a heater but I will be doing more to hold heat in next winter.

It also depends on what type of soil you're working with. If you can start off with wonderful soil you'll be ahead of the game no matter what you grow.