No. You would never call another woman 'buddy'. It's only used for boys and men. ....................... Meaning of buddy in English: used when talking to a man, sometimes in a friendly way but often when you are annoyed: Drink up and go home, buddy. [ as form of address ] US used by an adult talking to a young boy in a friendly and kind way: Are you okay there, buddy? [Cambridge dictionary]

من اینجوری استفاده تا به حال نکردم فکر نکنم درست باشه بیشتر برای مردها استفاده میشه

Yeah, the same way you'd use "hey guys" for a group of people regardless of whether they're male or female. Both are informal though.

hello my friend I am from Australia and we use it all the time here it is very common and acceptable. Some other expressions could be, Hey bra what's up? Hey my man (these are usually to greet men informally) Hey champ Hey mate, this can be used to greet a woman or man

Yes you can, but its not that flattering, if you know what i mean. If you are joking around and you have a relaxed type of relationship with your girlfriend you can use it as a joke, our in a humorous and fun/sweet way. Hope that answers your question.