The material that you currently have comes with FAP, and the other materials that you listed are floating around the net (guessing that the "free" is coming from that). If you are asking about what materials you should purchase, I would spend money on FL.
Next Step 5 FL = 150$
AMC Question Packs (FAP does not include all of them) = 72$ combined
EK 1-4 = 200$
Kaplan and TPR FL = 6 total that come with the purchase of the books. However, if you did what I think you did, you can get them for "free."
Edit: I would also check out Khan Academy as you probably already know. It is a free resource and very helpful in going over content and the passages that come along with it. The passages are very helpful for the PS section since there isn't much practice material out there for that section.
Best of luck in your studies.