I was thinking of teaching my child English as his first language, do you think that would be okay, or would he have issues stuyding Filipino later on?

Sharing the same thoughts with Lisville and Faye! My nephew's first tongue is also English. Whenever he interacts with other kids who can't speak the language well, there is a tendency that other kids refuse to play with him. He is also struggling with some of his subjects like Filipino and AP. He just recently had his summer class for Filipino. I suggest that while you let your child master the English language, still find the right balance in conversing with him using Filipino language.