The bike will work fine with that missing chainring tooth. There are so many teeth engaging the chain that one missing tooth won't cause any problems. If anything, it may actually shift from the middle-ring to the big one even easier with the missing tooth.
As for the chain-link, that most likely was caused by someone trying to re-use that pin after pushing it out. With the Shimano chains, a NEW pin must ALWAYS be used when the chain is disassembled by pushing a pin out. The ends of the pins are flared to grip the plates and pushing one out damages the flared ends and it never grips as well again. You can get a SRAM Powerlink to replace the one bad link. It's a nifty hand-installable/removable master-link:
http://www.samoht.com/weblog_img/powerlink.jpg
