1.) The pot does sound too small. 5 gallon buckets would have been better, but you really should try to refrain from doing too many transplants. Leaving them in the ground isn't a bad idea, as long as its the FINAL location. The advantage of growing a tree in a pot first is for easy planting in its final location later on.... rather the hacking away at
roots the spread through the ground. So ideally they would have been started in 5 gallon buckets, or dug up with the seedling was extremely small. If your not going to have the stump removed until next year, I guess I would put it in a bigger pot, once all the leaves have fallen.
2.) Central Kentucky should be fine to leave them outside, just keep them in a sheltered location out of the wind. Keeping them indoors might "trick" them into thinking is spring already. Which is bad. I had a potted tree in a
greenhouse one winter, it "woke up" and went dormant" 2-3 times in one winter. It died the next season. That's a lot of lost
energy lost. Make sure you keep the soil moist, but not saturated. It won't really suck up any
water all winter, but you still don't want anything to fully dry out.
Ideally you shouldn't transplant hardwoods until the leaves have fallen off in the fall, and the buds are fully set. The later the better, assuming the ground isn't frozen yet. If you dig up
trees while they are still active, their roots are extremely vulnerable. (softwoods by the way are the opposite, you should dig them up right before they become active in the spring)