The noise could be an anti-sway bar mounting point that is loose, a suspension bolt that is loose allowing slop, many things could cause that noise.
When you push down on the car, you are basically pushing against the spring not the AGX. The spring has more force than the AGX (RM are basically ~325 lb per inch of movement for front and ~250 lb per inch rear).
As far as lowering the car, Koni inserts (CSK) will not lower the car at all by themselves. The springs you run lower the car. The struts (B13) work with the springs to control the motion. If you want to go lower, you run a lower spring or a coil-over setup THEN you run a shortened strut so you have suspension travel with the lower spring.
If you have a street car, you do not need camber plates (unless the car is so low that you need to get rid of negative camber) - Ben only recommended them to help lower the car a touch while utilizing the rest of the parts you own.
Lastly, you do not need to fab anything to run GC coil-over sleeves on an AGX as pointed out. They will slide over, but there are tips on the forum to make them quieter, etc or allow you to run a wider tire (cutting the perch).
Josh