I agree with Jose and Kayla. I sometimes use the word "dude" or even occasionally "man" when addressing my sister ("Listen, man, I know what I'm doing!"), and I even sometimes use "dude" when addressing my mom, but this is very informal. Some girls will be offended if you address them with a term that's intended for men. It can work with close friends and family members.

It really depends on the person. If you're very close with them in a friendly way, then it would probably be fine. But it is slang, so there are no direct rules.

Stay warm. I am glad you reply me. Yes. I often online when I am free. You less activity on discussion I notice. I have cold too. Take care.

I would not recommend using it as a standard greeting. I would use it for close friends only.

Kinson, No, I am being sick recently. Wow, you noticed that I am not online lately. :)