Needing Advice! (San Francisco)

I will be 20 next month and I've been looking into aupair jobs in USA and a family from San Francisco invited me to come be theirs, I'm currently working in NSW for the public health system in a mental hospital - hate it. Me and my boyfriend just broke up so I though what could be the harm.. I need an adventure. I have only ever been to Bali.
I'm really confused and I want to get an idea if I will like it there before living there (impossible right?) but just to get some feedback from some Aussies that moved there at a young-ish age by themselves.
What it's like compared to australia how hard it is to adapt, just so I know what I am getting myself into.
I really want a different experience, and if I was to say that the only thing holding me back is being afraid that if it didn't work out i'd have to come home disappointed and go through the stuff of looking for a job again which I've kind of lost my adventurous side :( and I want to find it again. Honest opinions. Also the family offered me $450 weekly + free board + food. In exchange for about 50 hours a week of work, is that good?
Also I'm unsure of the kind of (what money can buy) standards there, whether to know if $450 is enough you know.. (which seems like it could be)
This is coming from someone with about as much knowledge as NONE! and google hasn't been helping too much.. :( any opinions would be greatly appreciated.
Thank you
x :)