1. You can ride on sidewalks. In fact, bike paths are on sidewalks! Mind that the japanese drive like the british, that is, on the "wrong" side and that stands for bike paths as well.
2. You can't get on public transportation with your bike, unless it´s a folding bike and has a proper cover. If, like me, you don´t have one, cheapest way to solve it is buying a big garbage bag, like this.
3. You can leave your bike on the street UNLOCKED! and nothing happens. At most, people use a wheel lock or a very thin cable lock, that you can buy at the popular Hyaku Yen Mise (99c shops) for that price, just to lock one wheel to the bike. Bikes are never locked to a post or anything, they stay that way outside all night and remain at the same place in the morning.
4. You can´t park your bike anywhere. If you do, you´ll get a ticket, likes these ones...
5. You can park your bike at free spaces for that purpose or you can pay around one dollar to park it in protected areas like this one.