A few would be an indefinite number that can vary slightly depending on what you're talking about, but generally is about three. I wouldn't call anybody wrong that used the term a few to describe any number from 2 to about 8ish. 10 is absolutely never a few though.
Next would be several, that would vary in the range of 4 to 12ish. Usually it would refer to about 5 or 6 though.
Past that it gets even more vague. You have "quite a few", or "a bunch", or "a lot". They all basically just mean more than several.
A couple and a dozen are different sorts of things, not fit for comparison because they refer to exact numbers. 2 and 12, respectively of course.