Hey, it's an all-or-nothing crowdfunding site. So if you don't raise all of the money you need, the funds are returned to backers.
They only accept creative projects and projects must be approved before going live.
R.e. your goal... You simply need to think about how much money you need to do whatever it is you're planning to do.
Not sure about creating two different projects but remember, Kickstarter are pretty selective about what projects launch so trying to run two will probably be difficult and dilute support.
Finally, how long it takes you to reach your goal depends totally on your campaign. Some have raised millions in a few days whereas others fail to gather any momentum. You need to offer great rewards and initially do some hard promoting to the people you already know.
I hope that helps!