Good luck with your new BP and welcome to the site! Glad that the lost snake has someone to take him in and that he wasn't found by someone who would harm him. Sounds like you're doing great so far and wishing you the best!
When you're checking for mites, it's good to check under the snake's chin (there is this little fold of skin there), the heat pits, around the eyes, and around the vent which are all places mites like to hide.