Biology: A lot of people think of bio as being an easy class and it honestly isn't that hard at SL, but HL gets quite difficult. However if you are good at memorising a 7 is achievable
Chemistry: Don't underestimate how difficult this is. The first few topics are relatively easy so a lot of students slack and then struggle when they reach the harder topics. This requires a combination of math and memorisation skills
History: I don't take this but I have heard that it's quite difficult and hard to get 7s or 6s in.
Math: Take SL. I took HL even tho I don't need it and it started affected my other grades because I dedicated all my time to HL math. I get that you're worried about having limited options but don't forget you need to have an idea of what you wanna do because your extra curriculars and essay need to add to that. Also if you're applying to the US, it's possible to change pathways whilst in uni, and if you change ur mind in the first month or two of IB you can change your classes.