The Philippines is a great country with very friendly people. I have relatives there and since we built a little vacation-house, we go there twice a year.
Raining season is between June and October. In Manila, there's usually a lot of rain during that time, but if you go further south, like the Visayas, the weather is quite ok.

In Manila, I like to stay in Makati. As the former poster mentioned, there are some very nice hotels. I've stayed twice at the Peninsula during the last 12 months and it's a wonderful hotel. It's very close to an area called "The Greenbelt", a beautiful park/shopping-mall/eating place.

Usually, foreigners are treated well, no matter where they come from. Filipinos are open-minded and outgoing. Although, if you behave like a jerk, they can become angry and unfriendly. So it's absolutely up to you how you will be treated. Most of them speak very good English, but if you talk too fast with a strong american accent, they sometimes have difficulties to understand you. They will never let you know and just give you a smile, but it's recommended to slow down a bit. Don't get involved in political discussions, they know that lots of things are not perfect in their country, but they don't like foreigners to comment on it.

I wish you a nice trip!