According to Henry Norr over at MacInTouch, an Apple booth staffer told him that although Apple does not recommend a the user upgrade the RAM, doing so will not void the warranty, as long as the user doesn't cause any damage. Supposedly, the hardest part of the procedure is getting the case open. If this is the case, then good.
However, wireless is definitely not a user-added option, although it can be added after the fact by an Apple Authorized service provider. According to Henry, you can add Airport Extreme and/or Bluetooth at purchase, but after purchase you can only add both together (as they come to the service provider as a combined kit).