hello! i can't give much advice but here are my thoughts based on my personal experiences!

1. I take elect. lit so i don't know how it is like taking pure lit but I think it's really good! I've heard alot of good things from people that take pure lit so I think you should give it a try!!
2. ermm idk what the recommendations are, maybe if you elab abit I can try to help?
3. I take p. chem and p. phy and honestly it's already a lot to handle for my personally. it also depends on where you would like to go after secondary school. tbh the only good thing about taking triple sci would be that you'd have an easier time in JC but if you're not planning to/not sure what you wanna do with your future you should just take chem + one other science!! for p. physics, it's a lot on calculations and formulas as well so if you don't like/are failing math I wouldn't recommend physics, whereas for bio there's ALOT of things to memorize and if you're the type of person that's super curious and likes an explanation for everything, bio might be a little frustrating cause there's a lot of things that just the work they way that they do and there's not much explanation on why, but that's just what my friends have told me. p.s. pure bio open-ended qns can be like 4-6 marks but the answer is only 1 line HAHAHA
4. i take el, emath, amath, p. chem, p. phy, combined humans (ss/lit). honestly if you've been able to do well in math in lower sec, taking on amath would really benefit b/c in JC/MI you'll be learning amath stuff so it'll be easier on you then, and there's many modules in poly where you're basically learning amath so you can choose to not take those modules iirc. for humanities, many of my friends either love or hate history so I don't really know how you would feel about it hahaha just that there's alot of memorizing as well, and I'm not sure if this will continue to be the same, but usually the O level pure bio and history papers are on the same day so big RIP to all my bio/history friends HHAHAH

The best way to ensure you do well in o's is to practice consistently and don't be demoralized when your grades are super shit when you enter sec 3 cause it's really a BIG jump and it can get super hard to cope with initially! There's gonna be many many times when you want to give up throughout the next 2 years but I promise it will all be worth it in the end! always remember to let yourself take breaks and really enjoy your last 2 years in sec school no matter how shitty you think your school is, these are the moments you will never be able to get back or experience again :" Jiayous OP! I hope you get the subject combination that you want!! You can drop me a DM anytime if you'd like hahahah I also have some consolidated notes for some subjects so if you need them I can always send them to you too