a few things:
1st:
the amount to bondo you used is a good amount when putting layer(s) on but I suject only to use 1/2 to 1 inch line for that amount b/c like CH09 said it hardens very, very fast. another amount people might try is this: 4inch diameter circle, 1/2-5/8inch thick with a dime(USD$) size spot of hardener. i found that this amount had about 3-4 minutes of working time and 10 cure time.
2nd:
i would suggest putting on thin layers, sanding with 100-200 grit (like CH09 said), and repeat this until you built up a 1/16 to 1/4inch layer (thicker layers were you need them). by layering, sanding, layering, sanding, several times, pin holes become very hard to find. spot putty doesn't dry very hard and is only meant for tiny air bubbles. only once you have the bondo smooth (like finished smooth) then sand with a high grit sand paper.
3rd:
Putting the bondo on cardboard is a great idea since it a cheap (and free). a better way to mix bondo is the getting the bondo mixing scrappers (they're pink). they are designed to work with bondo so when you are done and the bondo dry it just cracks off.
4th:
One suggestion might be to wear gloves when you bondo.
5th:
Primeing your pep after you fiberglass is another great idea that I have done as well. grey primer i think shows up flaws more so you can see where you really need to sand/fix but black will do fine too. the thing about autoprimer is that it is also a filler so it will help smooth out your part.
other than that good basic tut. could use a little more edit time to make it a little shorter and to the point.
also if people use a higher detail model (HD) the less bondo you need overall.