20gb is huge. Word, excel, will take 150years to fill up that space.
14.1" screen is standard size, there are 15" but 14.1" is the standard. It's fine too
256 is enough, more doesn't hurt, and if you can bargain double that for a little price, go for it. It's the cheapest upgdare you can have.
What to consider... Battery life is something, and expandability. Nowadays you can get pretty fancy laptops for a little money, integrated dvd-rom/cdrw devices, gaming graphics cards.. Whatever