the pac mans are pretty fat frogs, but if youre concerned he could do without the pinky mice for a month and just feed inverts. later you could work a small mouse in once a month. a lot of herps won't eat right away due to stress of a new enviroment. make sure the frog is warm enough amphibians cannot digest food if not kept at right temps. As for substrate they are burrowing frogs and need a deep enough substrate to burrow 3/4 of body. Peat moss without fertilizer kept moist not damp is perfect. if kept warm (78-85f) he should start eating right away they are not shy eaters hince thier nickname pacman.