take 4 subjects if you think you're a superhero then go ahead and take 5 hehe.

yes, unfortunately you have to self study. Ask your seniors around for a reliable tutor, and make sure the tutor knows about the marking scheme etc.

Maths S consists of 2 papers. Paper 1 is about 10 times harder than add math in SPM, i joke not Paper 2 is much easier, provided you pay attention to your teacher's techniques because there are rules and ways to understand it better. I got a C+ for paper 1 but A for paper 2 xD that's how different the two math papers are. Make sure you have at least a somewhat good foundation in add maths to try STPM maths. (and make sure you're hardworking too)

I did STPM English Literature too. Quite fun but stressful as there is no time to write. I live in Selangor so I'm not sure if my tutor's contacts would be useful to you.