I would go with the oiled foam. In the winter I use regular paper filter because...well...snow isn't abrasive. EBay will be your friend for the parts you need, you can also enter a WTB ad up in the trading post or on another site. You'll get whatever you need.
Now is the time to start reading up on 3120's; there are some accessories you'll want to consider if you will run in the cold. Also, a couple carb types if you are willing to anty up the coin.
Now you have to start saving up to have the saw Snellerized, Monkeyed, Masterminded or send to any of the other really good builders (and there are quite a few), who can turn that plain jane muscle saw into a monster. I sure love mine.