Essentials of racing?

I would love to get into racing but i don't know anyone who has. So i come to you great folks!

1. What gear is needed and how much should i be spending on it?

2. What kind of bike (cc and stroke) is best suited for motocross?

3. How do you get singed up for races? How is the system of races set up?

4. Is there anything you wish someone told you when you started racing?