As you've had him for less than a week, I wouldn't worry much. Just because he ate on the first day doesn't mean he's really settled in. Has anything occurred around him or been changed that may cause him stress? If he is in a room with a lot of noise or people walking around regularly, you may want to move him to a quieter, less trafficked area. I'd personally wait a day or so between feeding attempts to minimize stress. Your temp and humidity sound alright to me, but there are people here who probably have more experience than me with Pacman Frogs. Overall, I would just keep an eye on him and make sure he isn't losing weight or acting strange. Don't leave crickets running around unsupervised either; they could potentially bit or injure the frog if left for long enough.

Keep us posted on your little guy!