Not only can Japanese people tell if your degree is a fake, but they can deport you if you try to pass off fake documents as being real. Getting your degree for real is probably better than running the risk of being banned from the country for 5-10 years.
What kind of money do they use there?The yen (¥) is the currency in Japan. The exchange rate is around ¥100 per $1.
How big is Japan?The entire country of Japan is about the same size as California and around 75% of it is mountainous. The population is around 126 million (about half of the United States), so it can be rather crowded in some areas.
Is my driver's license valid there?No. If you want to be able to drive in Japan you will need to apply for an internation permit. It may however, depending on the length of your stay, be easier and cheaper to just use the available public transportation.
Is it true that all Japanese people speak English?Actually very few older people in Japan will speak any English at all. You may find a few younger people that can understand you, but it'll be much easier to get around if you take the time to learn a little Japanese before you go.