Like get some from Tractor Supply. That's a great idea!!
One thing that I would recommend when integrating the store bought chicks with mom is to do it in the middle of the night really quietly - not to disturb her. Also if you have fake eggs put them under her so that she thinks they just hatched.
The egg looks healthy - if the chick is moving like it is normally it is healthy and doing well. It looks like it could be on Day 14 - 16.
If you don't mind my asking - What are you planning to do with the baby??? Leave it with mom??