Depende kung anong gusto mong gawin, no? General photography or do you have any specific interests? Anong budget mo?
Kung bago, they all really have the same sensor, except for the D3X - 12MP, so that's not a defining feature.
Medium class - well, that could put you in D90 or D300 land. Clear differences in build and features - pero defining difference is of course the ability to shoot video with the 90.
12MP is large, so I wouldn't go with anything less than 4GB cards. Stick to Sandisk and Lexer kung pwede. Reduces the uncertainty of being compatible. If you're planning to shoot video with the cards, kailangan Class 6 (which is an entirely different rating system than the 80x, 133x, etc).
Start with the lens that comes with the body if possible. Then usually people go two ways, bibili nang telephoto or an external flash. Kung telephoto, madaming choices, or meron kang lumang Nikon lenses, baka compatible pa. Kung flash, kailangan iTTL compatible para gagana nang lahat nang features, so that makes it an SB-400, SB-600 or SB-900. Kung meron kang makitang SB-800 on the used market, pwede rin.
It does a good job of explaining the various terms like AFS D ED IF DX etc.
As for zoom ranges, it simply means what type of view can you expect to see using the lens. For example 18-200 expresses a wide range of views - 18mm is considered wide-angle while 200mm is very telephoto (so you can reach out and see distant objects closely). The best way to understand this is to view it. I found this simulator on Tamron's website that visualizes the differences very well. Use the slider to see the differences in perspective from wide all the way to 500mm...
Use the Red and Black arrows to set the beginning 18 and end 200 and you will see exactly what you can and cannot take in a given photograph. You can even change the photo to see how it works with different subjects. Very useful.