I think DS5 went as far as liking timeouts since he could watch the timer on our microwave
![smile smile](/bb/images/graemlins/default/smile.gif)
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.