Black Locust seedling care and transplanting

I have one black locust (BL) seedling that germinated this spring and is in a smallish pot about 4" diameter right now. The tree is about 12" tall.

We're in SE Manitoba Zone 3b. I want to try and over winter the BL seedling in a larger pot or container, and transplant it out to its permanent location in the spring.

For the good knowledgeable folks here, a few  questions:

1. I want to pot it up to a much larger container, maybe a 3 or 5 gallon pail, to overwinter in. Should I go that big?

2. Any suggestions for the soil to use? Would I be correct in thinking the soil should come from the ground near where it's going to be eventually planted? Maybe with some compost added? Or any regular potting mix ok?

3. How to overwinter the BL? My guess is to set the potted tree it in a protected area outside where there's shelter from wind good snow cover, at least. Should I partly bury the container? Mound snow over it? Wrap the seedling with something once it's gone dormant this fall?

TIA for any help!