First off,
get your rabbit neutered.
This could possibly solve half of the issues that you are currently having with him. It's possible that some of his destructive behavior is being driven by hormonal frustration, and neutering could at least calm him down some.
Next, rabbit proof. If your rabbit can destroy anything in his area that you don't want him to, then it isn't really rabbit proofed. This means that anything in the area where you want to keep him, needs to be impervious to him being able to destroy it if you don't want him to. If he's in a pen, that means flooring that can't be destroyed. Sometimes a sheet of lino will work, with all edges outside of the pen so they can't be chewed. But some really determined rabbits can manage to destroy lino. If your bun is like this, then you would have to use hard flooring such as ceramic/stone tile, concrete, or horse stall matting.
You will need to escape proof his pen. Best way is with welded mesh wire with 1/2-1 inch spacing. I prefer the 1/2 inch so they can't chew or pull at the wire. If you need to make any cuts in the mesh, make sure to use flush cut pliers or other cutting tool that can make a flush cut of the wire, so you don't end up with sharp nubs at the cut. And believe me, they are sharp! I also like the vinyl coated mesh the best, as the cut edges don't seem as bad with it.
If there are bare walls in his area that he can get to and chew, then you will need rabbit proof wall coverings, which would be sheets of plastic. There is a vinyl wall panel like this that might work.
http://www.lowes.com/pd/Sequentia-4..._clickID=37941310-fbc9-4584-a146-9a11af627dfa
Or clear acrylic sheets, like that used in windows. Just something that little bunny teeth can't get a hold of to rip or chew.
Next is solving his issue with being scared, freaking out, and injuring himself. I would suggest to stop fostering the kittens. It is obviously frightening your rabbit and he could end up with a serious injury as a result. Cats are predators, so it's not unusual for a rabbit to be terrified of them, even to the point of it causing cardiac arrest. And I have to disagree with the above comment. No, rabbits are not tough. If he keeps freaking out and running into the sides of his pen, you risk serious injury to him. Things like a fractured jaw, head injury, or spinal injury. I know of rabbits that it's happened to. Some have had to be pts, some have needed an expensive surgery to wire their jaw back in place. So trying to prevent this from occurring is essential.
I would also add a bunch of hidey holes and tunnels to his area, so that if he does get frightened by something, he has somewhere handy to bolt to instead of into the sides of his pen where he could get injured. You can use something as simple as cardboard boxes. I would give him several and cut both an entrance and exit hole in the box, as rabbits prefer this so they don't feel trapped or cornered. I would especially put them along the edges of his pen, lining the edges as much as possible so that instead of running into the pen when frightened, he has a tunnel or hidey hole to run to.
After you get him neutered keep in mind that it can take 4-8 weeks for the hormones to completely fade, so don't expect any immediate changes right after his neuter. Then after 8 weeks if you still are considering finding a friend for him, read up on bonding rabbits as it can be very complicated and isn't always successful(in which case you could be left with 2 single rabbits). Then find some rescues/shelters in your area that spay/neuter their rabbits and allow you to bring your rabbit on a 'date' to see if there are any potential friends that he might get along with. Not all rabbits like each other, so you want to be able to find one he might like before actually bringing the rabbit home for bonding.
Jbun
Health and Wellness Moderator