1) It's all about knowing line weights and becoming REALLY friendly with the pen tool. I can't really explain it, but the thick black outline that surrounds everything is basically achieved when you grab the basic shape of the piece, copy it, paste it behind and then increase the stroke to something large (I believe this was a 9)
2) It's all vector based so there is no need to worry about resolution.
3) My most common settings are the most common settings on AI. I always have my tools, text, gradient, stroke, color swatch, pathfinder, and info boxes open.
4) I'm not sure I understand the question, but as I've said before...I'm not a fan of layers so everything you see that I've done is always done on a single layer.
I'm actually in the process of having my "average joe" screen printed on some clothing items I designed. I doubt anyone other than my friends/family will wear them, but what the hell.
Hope this helps.