Welcome to Philippines, for you being a diver, you can choose several diving destination in the country, places like Batangas, Mindoro, Cebu, Dumaguete, Bohol, Boracay, Camiguen Island,or some part in Mindanao, just avoid the areas heavily populated by Abusayaf (Basilan) they are known bandit that kidnap tourist for money. But don't worry, only less than 10 islands in the Philippines are in trouble, and still we have 1,100 island for you to explore.
You probably enroll in a dive shop to work with your diving skills to Professional level as diving Instructor, to make returns of you diving investment.
Food, we eat rice, barbeque, roast pig, and many delicious food which is rich in cholesterol and i am sure you will love our San Miguel beer, but don't worry about food, it will never become a problem for tourist in Philippines, they can get what they need. Their are big Malls in the City and the beaches that have diving facilities, normally have restaurant that serves international foods. The food prices are much higher compare to Filipino standard, food cost, you can pay for 1 to 3 US$ equivalent per person per meal.
The only problem some tourist experienced in our country is women, specially in the bar, they are beautiful that some times you forget you are draining your pocket. I advice you to make reserve fund to pay back home.
Accommodation, you must rent small houses near the place you can go diving, stay low to survive for two years, house rent can be 100 to 300 US$ per month, but if you decided to rent a hotel room that will be around 50 to 500 US$ per day. We have big hotels and casino, Shangrilla Hotel, Hilton Hotel, Marco Polo Hotel, Water Front Hotel, and Marriot Hotel. Still many to mention... This hotels are located in the City.
Filipinos culture are very open, not reserve specially on the big Cities, only the Muslim area and the Ifugao at mountain province have pronounce culture, but mostly can speak English, or at least you can communicate easily with most Filipinos if you are not particular on the English grammar, then it won't be a problem.
You need to adjust the hot environment, you can wear short pans and sleeveless shirt, or plain t-shirt. If you go to the City or planning to have a date, blue jeans and polo shirt or printed t-shirt will do. Never wear Tuxedo in the street, you will die with heat stroke, just use it in a very formal executive meetings.
Most Filipinos are low profile, and many of us are living in a very low income level, but we are very friendly, Filipinos are very sensitive so please try to avoid barking with them like dogs, and avoid to make fist fight to win what you need or discriminate them badly, the next thing you know they bring a gun, just talk to them softly, you can win their friendship.
Always smile, you can have million of acquaintances, and friends... city crime and drugs are common, so make a research about Philippines in the internet, "Lonely Planet" travel guide to Philippines will be your best guide references to explore our country.