Hi Skooter, he sure is a handsome boy. I think you are so wonderful for taking the time to protect him and nourish him. I read Catty1's post below and it sounds like you really saved him from a miserable existance. I know it must be so hard to have him in one room and your cats in another but I was so relieved to read that he was no longer outside and vulnerable to the people who throw things at him and the maintenance people who want to trap him and then do who knows what to him!
I hope you will be able to hang onto him until someone in your area can help. I wish I could do something but I live in Canada. As Freedom mentioned, if you can get a can of the calming spray (which is available at PetsMart and Petcetra and is cheaper than the version sold at vet clinics) it might help relax him so he's not feeling so aggressive. It might just be that he knows you saved him and he wants to keep you and he may think your other 3 cats might jeopordize this.
If you can pick up some Rescue Remedy at the health food store you can put some in his water or food (check with the health food store for dosage) and it should also calm him. These are not drugs and could make the time between now and when he is able to get to that shelter easier for you and him and your other cats. I do hope that you will find a way not to put him back outside though. Hang in there!