"Hey" always sounds like an "ahoy" to me, not really a greeting. It's little bit like yelling, "Oi! You!" at somebody. Hello means hello and good morning/afternoon/evening all convey a pleasant greeting to anyone you meet.
Oh, this one cracked me up because when I thought about it, I realised that due to my *excitable* nature, I can sometimes sound like Mrs Doubtfire, face covered in whipped cream, saying, "Heelllllllloooooooooo", and then have big hugs all round. LOL. I am much more sedate, polite and hand shaking under other circumstances. Bahahahahahahahahaha. No wonder my dogs get so excited when we have visitors!! Gosh, these questions can make you have a look at yourself. I love them!
Hello to people I don't know usually, but if I am in a cheeky mood I say G'day with a smile.
G'day is also used for people I am close to . Sometimes I respond with Hi, but I don't say Hi if I am the first to speak.
Funnily enough, I rarely greet my friends with any of these words. I'm more inclined to say their name and kiss or hug, or both. For people I don't know and are being introduced to, it's usually "nice to meet you".