Nice guide, I finally learned what vignetting is...
I did a quick read through so I may have missed it, but you didn't mention anything about filters
I've worked without any filters for a few months, but now I've equipped all of my lenses with cheap Hoya UV filters for protective purposes (especially the macro lens, since it gets close up to objects). I never had a problem without the filter, but it's certainly a nice way to protect your lens, yeah?
Actually, before I got my filters I'd use my lens hoods for the purpose of protection (just so that nobody could bump into the lens or anything). Only later I found out that lens hoods are supposed to help block lens flares and slight excess light
My only filter experience is with a Hoya UV single-coated filter (cheapest) - I don't know whether multicoated or any of the fancier ones that cost 6x as much are much better. I've read that the UV filters can cause some reflections when taking pictures in low lighting, but have yet to test it for myself.
But I'm being unfair - your guide is for buying lenses, and it's a superb guide for that. I guess I'm craving some of the more technical details that I still don't understand or have just mastered (aperture, lens care, etc.)