You are lucky to be able to go to Japan at a young age, but old enough to really appreciate it.
For starters, it appears that the main train between Tokyo and Chiba is the Sobu line. I've never been to Chiba, so I could not tell you what to do there.
But the main thing is, since you have several months to study up on things before you go, get yourself some travel guide books and
maps. One good source is the Japan National Travel Organization (JNTO). Their website is
JNTO. You can get free maps and guide books from them. They have an office in Sydney and there's a link to it.
I am sure other JREF members here can steer you to other sources for info.