How many Star Medals are there in Super Mario 3D Land. I've gotten 350 so far, but I've seen two more (I couldn't get them from the mystery box in time). There are 281 in all the levels, so is there an actual limit to the number you can get, or can you continuously build them up?

There actually is no limit, I believe. As long as you can get new Mystery Boxes via StreetPass, your Star Medal count should be able to max out to 999. Could be wrong, though.