Syllabus is the things to cover. Past papers is a test to check what you have covered.
Start with Islamic studies and GSA as these two are comparatively straight subjects. Follow their syllabus as mentioned by fpsc. Give yourself 7-10 days and see if you have covered a portion of each. Then get past papers(actually past papers should be by side anytime one studies) and see if they contain any questions from portions that you have covered. If yes, then try to answer these questions. If no, then it means you need to enrich your notes.
In this way, your preparation will remain on track and even no need of academies etc.

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