i need to replace my clutch , and am thinkin of upgradin to a stage 1

1. do i need a new flywheel?
2. how do i know if the flywheel i get is compatible?
3. what is the diff between stage 1 and 2?
4. what will a lighter flywheel accomplish?
5. why is a stage 2 cheaper than a stage 1?
6. would i be ok puttin a stage 2 in ?

thanx for the help in advance fellas!