How many SAT subject tests (SAT II) should I take? Can you take more than 1 language in one day?

Hi im a high school junior from canada and just wondering how many sat subject tests i should take. Im pretty sure I can do well in about 7 tests, but it takes way too much money to take as much as I can. Im in IB, which is sorta like AP, so should I not take the subjects that I'm taking here? They are Biology and Math, probably Lit, b/c thats like english... And for the language I have to choose between Korean (my mother tongue), Japanese (IB honours course) and Chinese (which I will just get normal gr12 credits) for the language one. Which one should i choose, my weakeast (chinese), my mother tongue, or my next strong language (japanese). And can I take 2 language subject tests at the same time? I missed the last November ones.. More Sat IIs the better?? Thanks a lot =)