Yes. It's a subtle insult that means someone has to many opinions about everything. This term is usually said to women in Western societies because traditionally, women were expected to not question things as it was not "ladylike" or "proper". It can be said to anyone nowadays, however.

Yes, it is. It means "characterised by conceited assertiveness and dogmatism". (Oxford Dictionaries)

Not technically but yes, it is a more derogatory way of saying that someone has a lot of opinions. It has a negative 'feel' to it. But occassionally it is not used in a negative context.

Yes. Saying someone is "opinionated," describes them as having a lot of their own opinions which they find to be the best. They won't follow the advice of others, because they tend to think that their way of doing things is superior.