I plan to do oil changes myself as well. Since it would be under warranty, I would stick with Mazda OEM oil filters. From what I have read on the Mazda 3 forum, the filter is pretty good. Buy a half dozen from your local dealer. Don't go to Walmart and get cheap Fram or Quaker State filters(not knocking Fram, just cheap filters) As for oil, 0W20 GF-5 certified. Castrol and Mobil 1 0W20 oils are certified GF-5. I prefer synthetic, especially in winter. As for drain plug, most require a new washer after every drain. Invest in a torque wrench set to not damage the threads.