Rookie, are you sure you should be installing your own gears?
Sorry, just a poke. all kidding aside.
#1 don't use so much marking compound. just a light solid coat on 3 teeth will be pleanty. that way you won't get it all over the place and it makes it easier to attain a pattern.
#1 turn the ring gear into the pinion. if the pinion is properly preloaded then it will take some effort to get it going. this will give you a better pattern that is easier to read.
#3 when you take a picture, pull the camera away and get the whole diff in the shot. I like to see the residual pattern, the pattern made when the pinion applies compound to ring gear teeth other than the 3 that you had originally applied the marking compound to in the first place. not to mention that when you pull back, your focus works better and I can see more detail.
#4 Yes you need to spin the gears in both directions to get a pattern on both sides of the gear.
#5 set your camera to a lower resolution. 640x480 is pleanty big and it loads faster.
#6 Add .003" to the pinion shims to push the pinion a little bit deaper. open the backlash up to .007" and take a better pattern.