Fukuoka has an international airport with direct links to most major destinations. It has a port, is on the bullet train network and a long-distance bus station. Some basics You need a passport and in principle, a return ticket. You should also be carrying sufficient funds to cover your time here.
Most countries can get a visa on the spot in Japan - but check first.
Wear a tie and look smart, particularly if you are young. It WILL ease your path through immigration. The Japanese are considerably better dressed than scruffy westerners and judge you on the basis of how you dress. Porn - it will be confiscated as a threat to the nation's morals. Besides, the country is 3 foot deep in it already.