[@ShwiggityShwah]

I haven't really given much thought about possible clubs Miki and Hiroki might share, but they're probably in at least one together. 

[@The Irish Tree]

After thinking it over, I would imagine Miki and Haruka would at least know each other (as students, at least), and perhaps might even be friends.

[@Alliance Oda So]

As for San, I'd say they might be aqquainted, but probably not that well. Then again, they could be friends. Miki's easy going enough to befriend pretty much anyone, really.  What do you think?

Don't really know about the other characters yet.