Its great that you are trying to inform people, but I do take some of it with a grain of salt. I will point out where I find points that should be revised:
"a quality 500mm lens (the best for bird photography)" - no, the 500mm is a popular one, but the 600mm, and 800mm (gaining popularity among avid pros) are just as good. I notice the reference to a lot of zooms. From my opinion, zooms are not worth it for quality photographs. You will always be at the higher end of the zoom range, which will always suffer from lack of sharpness. I have a Canon EF 500mm F/4 prime and its the best lens for me and my system because of many considerations. One being that its lighter than the 600mm, and it was more affordable, handholding possibilities are there for a small amount of time, and its optically fantastic. Way better than my 100-400 at 400mm in terms of sharpness and its image quality is great. I cannot speak for Nikon users, but I'm sure that the lenses are just as good, but also unjustifiably more expensive than Canon's. And yes, its big, heavy and awkward, but birding isn't about chasing birds, its about them coming to you so you can photograph them naturally.
In addition, you will almost always need a 1.4x teleconverter, because the birds are never close enough. You will lose autofocus on any of the zooms (except the 200-400mm VR from Nikon I believe) and that is useless in bird photography. The autofocus is a key component to capturing great shots. I wouldn't recommend going from a D50 to a D90. Its hardly worth it for what you get. If you can grab a D200 or D300, you will be better off in that the autofocus is WAY better, and you will have a much better body to withstand the weather conditions.
Another thing no one talks about is a blind. This year I'm making it my mission to photograph the belted kingfisher and to do so I will need a blind. There isn't any lens that will get me close enough that the bird will not fly away, so the use of the blind is imperative. And its the best way to catch the birds doing what they do best in a natural environment without feeling threatened.
Just a few points you may want to consider