A 10 gallon tank is fine for a baby bp. You'll want to make sure you have hides on both ends of the tank and that you're able to keep humidity up to proper levels. That's the biggest usual complaint with glass tanks and screen lids is that it's nearly impossible to hold in humidity. Do some searching in the husbandry section. Make sure to read the caresheet from this site so you know how to create the ideal environment for your bp.

And YES, it's always better to buy at a reptile show IMO. There will be multiple breeders to choose from, a MUCH larger selection of animals than you will find at any big box pet store, and the animals are most likely going to be cheaper and in MUCH better health at the show than at a pet store. You will have a chance to talk to the breeder that produced the animal and ask questions like what it's eating, when was the last time it fed, what are the genetics of the snake, etc...