I would put the bunny and cage in a very quiet part of your place with a light sheet partially covering the cage to help provide a sense of security. Then disturb the bunny as little as possible for the next 48 hours. Only checking to make sure bun is eating, drinking, and pooping ok, and seems alright. If the bunny is eating/drinking ok but still seems scared after that time, it's going to take some patient work to help your bun feel safe around you.
I wouldn't be giving any new foods that he's not used to. You need to stick with the same exact foods he's used to, at least for the next few weeks until he's settled in well, then very gradually make dietary changes. Exception would be that it's ok to add a free fed non grain grass hay, and if his current food pellet is causing severe digestive problems then changing that would be necessary.