I'm thinking of getting Eagle 079 series 20x9.
The BS is 4.66 and Offset is -12

Question:
The BS tells me they will stick out about inch and half to 2 inches?
what will the -12mm offset do.
Does it make it stick out further or less.

Or since these are 9 inch wide they wont stick out as far as a 10inch would have?

 

BS and offset are just two different ways of measureing the same thing. THose wheels will stick out about 2.5 inches farther than your OEM wheels. As for how far a 10 inch wide wheel will stick out, that depends on the BS/offset of the particular wheel.