Your study permit will be valid for 9 months (6 months + extra 90 days). You will also need to get a Co-Op work permit at the POE.
PEBC Evaluating Exam is a pre-requisite to be accepted into the CP3 Program so you would have to complete that first before applying. PEBC Qualifying Exam can then be done either during or just after you complete the program (depending on the session)