looks like you've been doing your research on craigslist.
every motor bike for sale always says "150mpg, 45mph, no license required!!!"
realistically, expect between 75 and 100mpg on average. a well tuned motor will give you more, a poorly tuned motor, less.
speedwise, stock out of the box is about 30-35mph.
and you DO need a license in California. check this thread:
and this one:
don't let any of that scare you off, though. these things are super fun...