Keeping his setup as much the same as usual can help. Also if he is comfortable with you, then spending some one on one time with him once in the new place, can help add some security and help him feel safer in his new environment.
If he isn't used to cats, I wouldn't even let the cat in the room initially, as he should have some time to settle in and feel safe in his new home. If at a later time you want to let them meet through cage bars, then it may be ok to try, but I would be very cautious as some rabbits panic around predators and he could injure himself if he does. If you do attempt an introduction, they should always be supervised. Also keep in mind that cats can carry deadly bacteria in their claws and teeth, and a bite or scratch has been known to cause a fatal infection in some instances.