RAM: Very easy to install, but very cheap to have it installed for you.
Screen: The resolution of the two sizes is the same and images on the 12 will be just as crisp and sharp as images on the 14
Mhz: 800 is good; 933 is better, but 1ghz is best.
Discounts and shipping: Not really sure about Japan's or Canda's purchasing/shipping fees or how they would do something like what you're needing, but I'm sure that Apple could get you an educational discount anywhere in the world.
Friends laptop: Is it a Mac? or a PC? Because annoying pop-ups are usually related to PC's.