They will probably fight with each other. Cats are not like dogs, it isn't really a good idea to try to introduce "playmates" unless they are staying permanently. They aren't pack animals and even though at one time I had 22, there were still those who preferred to stay in their own "safe zone". Some would buddy up, but mostly siblings.I am curious how he'd react if a friend brought her fixed male cat for a visit though.
Not only that, but if you make him feel threatened, he may start to spray to mark his territory. Tom cat urine is nasty and if he doesn't do it now, whatever you do, don't get him started.
I have always had at least 3 or 4 (22 was a bit much, but wasn't really my idea, people kept dumping pregnant cats at my house. I was getting them fixed and "was going to" find them homes. Well, I did. Mine) Anyway, I am the proverbial cat magnet. If there is a stray, it will come to my house. If I go anywhere, they come up to me.