Taking 6 CLEPs in one semester?

[STW87]

I've never taken any of the exams before, but I want to take 6 by the end of the semester (while taking three classes) so that I'll be considered a junior. I'm studying for the Human Growth exam right now and I plan to take it in a couple of weeks when my classes start. Others I plan on taking are Western Civ 1, college mathematics, chem, bio, and possibly the statistics Dantes. I have a little over $600 already set aside for this (the price of taking one 3 hour course at my university) so I'm serious. I'm using the instantcert study guides.

How long should I give myself to study for each exam? I'm a psych major and already took Lifespan Developmental, so I'm confident about Human Growth. Bio and chem I'm not so good at, while mathematics and statistics I'm familiar with, but in need of studying. Western Civ I'm not familiar with, but I don't think it'll be too difficult.

How many questions are on each of these exams and how many do I need to get right to pass? Thanks!