well there can be problms but there are so many good times with cats too. oh I understand now, your cat and his cat. maybe you should give them some time to adjust to each other and a new house before bringing in a new kitty? can the kitties meet a time or two before moving in to the same house? your cat and his cat might both feel misplaced at first, since they are not in the same house anymore, I mean, it's not like a cat adjusting to a new cat in his same home. maybe it will work out better that way...
well good luck, keep us updated on what happens