I can't answer all your questions but I can get the ball rolling and I am sure some others will take it from there.

Regarding # 1:

I didn't take any shots at all and I know many who don't. If you are really worried then just ask your doctor. Perhaps the OZ government has a website from their department of health that can tell you what shots are suggested. BUT, most forego the shots and have no trouble at all.

#2:

By all means take a camera and lots of film. If you plan to ask your GF to marry you then it might be a good idea to take any imigration forms necessary. It'll be hot there so take some light clothing and it will also be bright there so take some sunglasses. Take some pictures of home and family to show. Don't forget the hoopsnake repellent and the viper rat repellent which may not be available in Australia but don't worry you can buy that on the plane through the duty free service provided by the airlines. Take an open mind and a respectful attitude. Take any medications you need. Might want to take a probiotic and garlic supliments.

#3

I'd not worry about her coming for a visit because tourist visas are very difficult to get and usually require a rather large sum of money on deposit or coming from a wealthy family to obtain.

#4

Be patient. Be understanding. Behave yourself. Treat her like a lady. Be friendly. You mentioned cooking them an OZ meal, perhaps but they might take it to mean that you are not enjoying their provision. I wouldn't even suggest it. Just go and enjoy the Philippines, its culture, its food and its people. It is a remarkable and beautiful place. Listen to your GF and her family when they make a suggestion because they will be concerned for your welfare and safety and it is their home, they will know where to go and when to go.