should I only focus on my English courses if that's what I plan my major to be? or take AP math courses as well?

I'm the one for shooting your shot. When it comes to AP classes, it can be any subject, but make sure whatever you choose is something you can handle. If math is not your strongest area, I do not recommend being in AP math. Taking AP English courses can also help with your major, in the long run, is better suited for you since that is what you want to major in.

The more AP tests that you pass, the less time you’ll spend in college. At my school: 100% graduates with some credit, 70% earned enough credit to finish a semester early, and 35% earned enough credit to finish a year early. Finish college and get a job sooner. Taking more APs will only be beneficial.