I think DS5 went as far as liking timeouts since he could watch the timer on our microwave
His number obsession wasn't as strong as your son's, but he sure has gone through quite a lot of obsessions. The good news is that he time learns a lot from that.
I too don't think that boys under 3 are too social, I used to be worried about it as well, but preschool made a great difference for DS5. If you are worried about social skills try one-on-one playdates. I think those work better, especially for shy or introvert children.
