OMG.... and that is why pet stores make me very very angry...... i feel like that frog would have died in there in a next few days and you guys have rescued him, I'm sure he is lucky to go home with you and that you try to save him.

I wouldn't wait until he is settled, it is crucial to get food in him asap, feed him, but small crickets, not pinheads, but he might not be strong enough to eat, you need to react quickly, give him a few crickets and see if he is eating, if not, force feed right away, small piece of nightcrawler coated with reptiboost. cover all sides of the enclosure with something, anything not see through. right now MBD or anything else is not a concern, he needs nutrition asap, everything else can wait a little.
i would report his state to spca though, it won't change anything but it might force a store managers to think a bit more.