Hi! I lot of people would disagree with me but I prefer the 2 liter bottles to milk jugs. Don't know why...they just worked better for me. My dh cut them in half for me (with a power saw...think Tool Time) and then I took the top half and cut three long triangular wedges out so that they would slip down on the bottom half easily. You can gradually slide the top up to provide more air circulation that way.

Prepping the bottles this way allows you to have at least 3-4 inches of planting mix. The roots on winter sowed seedings get big and long. That's a good thing. I had some shallow containers last year. I won't this time. They were way too hard to keep evenly moist and I lost most of those seedlings.

As for the height on top - not so important. By the time most of the seedlings get a couple of inches tall you will probably take the top off anyway. They don't need to grow up to mature size in these containers. If you want to grow them out more, transplant (they will need thinning anyway) them into small pots. I'm planning to do this with hollyhocks so they won't be so tempting for the bunnies when I put them out in the beds. (Experience talkin' here.)

I put my wintersowed containers on a part of my deck that gets partial shade...especially later in spring. There is a tree that grows up through the deck and as it leafs out it casts more shade on my containers. PERFECT! If you don't have that kind of set up, you may want to move your containers. You are in TX so you are going to find that keeping things moist in spring is your big problem. It will be fine during winter but in spring when the temps start going up and the sun is stronger, things will tend to dry out and that is a pain keeping all your babies happy. A little shade is a good thing. I would try to adjust plants that go into full sun before putting them out, though. Even if it means watering almost daily you don't want to sunburn the little darlins with an abrupt move into full sun. As long as your containers have tops wind and ice should not be a problem.

I can't answer the part about stratification. But maybe somebody smarter than I am will be along to help with that.