Lolx...In my opinion, it is no harm for you to think of taking a double degree in business and law. That would depends whether do you have the intention to practice in Malaysia. Please refer to Legal Qualifying Board , if i am not mistaken, for a double degree holder, the duration of it must be at least 5 years, with that, you will only be allowed to sit for CLP . So, though it is no harm to think more, you really have to take more things into consideration before you make any decision.

Due to the A-levels subjects issue, if you are capable with 4 or 5 subjects and score well, why not ? it opens more options to you.
If you are not, 3subjects is advisable. Actually, whether those subjects are the best option is really subjective as it depends on how do you define BEST in this context. Anyway, the aforementioned subjects are commonly what pre-law students would take nowadays.
Besides, if you think you can do well in science subjects , you can try taking it. Why not i mean if it helps you to get an A instead of others subjects which are total stranger to you ?

My 2 cents. Hope it helps. hehe...