First of all, what is your career path that you wish to pursue in the near future or you are still unsure at the moment? In my opinion, STPM really moulded me and it's all about working smart not hard, though.

Arts student here, i took all the subject u stated above except B.C cause I had Maths M.
I did not go to any tuition for STPM and got 2.5 ( not good but better than the one who goes for tuition). I had no accounting background and manage to pull a B in total. It depends on you and also u need to see which teacher is teaching u

1) If you are not sure about what you wan 2b in future, go for Form 6, as it's d most economical & safest choice. It's d cheapest pre-u course around & provides many options towards pursuing a degree, either locally or abroad, private or public. 

2) If u intend to study STPM Science, you'll be able to select a course from a wide range of choices. STPM Science students can choose either Science or Arts courses in universities. For example, STPM Sc. students can apply for Sc. courses like B. Eng or Arts courses like Bachelor of Management. STPM Sc. students are oso given preference during d university admission selection process. Many university courses are Sc. related courses, so Sc. students stand a better chance of entering public universities. However, STPM Science subjects are vry challenging & if you dont have a strong foundation in Maths & Sc, you'll have to work extremely hard to get decent results in yr STPM.

On the other hand, if you hate doing maths and calculating using those scientific formulas, Arts stream is for you. STPM Arts stream is mostly about reading your textbooks and memorising its contents. 80% of exam questions come from textbooks. STPM exam questions for Sc. stream like Chemistry, Physics, Maths T cant be answered just by reading textbooks. You'll nid 2 understand d concepts and calculations inside textbooks before you can answer d exam questions correctly.

3) Attend tuition classes if your teacher teaches you answering techniques or if yr teacher marks STPM papers. You'll be able to tackle d exam questions effectively & avoid making common mistakes STPM candidates make.
Go for Science if you:
-Just want to enter university, like many of my friends who dont know what they want. (lots of choices if u r frm STPM Science when u apply to public universities via UPU)
-Love Math & Sc., as it involves lots of calculations & formulas.
-Want to challenge yourself, because STPM Science can be very taxing.
Go for Arts if you:
-Dont want to be involved in Science related fields, like medicine, engineering, etc.
-Think you can scored a better CGPA by studying Arts.
-Want more free time to relax or have less stress.