First off, welcome to the board, and to answer your questions:
1) Yes, the guys here are awesome. I look up to them too.
2) You can scratch your armor with knives or carve it slightly with a dremel, but those might be a tad dangerous if you're not careful. You could also throw it against concrete or gravel as Jax does, to chip away some paint. Or, you could fake it by weathering it in the painting process. This generally takes a few layers of paint to accomplish, starting with a base coat which is usually silver or hammered steel in color. After this, you mask off your armor in "damaged" sections, and then paint over it in a new layer of paint. Once that new layer is done, take off your masking material, remask it to include the silver you kept untouched as well as a border of the new color, and then paint a new layer. This will make it appear as though paint has chipped off, though in reality, you just kept it from being painted on.
3) Yes, mustard can really be used. I was skeptical, too, until I used it on a small tin. It was a test piece, and it now sits proudly in my car as a pen holder!
Yes, any type of Yellow Mustard will work... just make sure to wipe / wash it off between layers, and dry off your armor before masking with the mustard and painting again. I dunno what "guy" you mean, as the mustard method has been used by a lot of people on here and in the costuming community in general.
4) Yes, Alan is a treasure for his work... but don't forget everyone else who puts in their hard work, too! Like 99Cent, Skup, Fettpride, RussRep, Ruffkin... tons of people. That's just naming a few. Massive respect to these boards.
Any more questions?