Malcolm brings up some good points. Doing this works for me because I was a photography major in a previous lifetime and knew all the particulars about doing photography with a manual lens.
With your old lenses do the research and confirm what will and won't work with the D90. Unfortunately, to get auto metering with many of the older lenses you have to go up to a D200, and you can get a really nice macro lens for the price difference.
Yes, your teleconverter probably needs to be used in manual mode; I did find one set of extension tubes that works with automatic lenses, but it costs $165 for a set of three.
Reversing the lens does seem to work well for me, but I can only use a couple of my lenses for that. My 300mm lens has a 72mm filter thread, so I'd need a different reversing ring for that. DH's 70-210 zoom I think is a 62mm thread. My 135mm lens doesn't work at all due to the placement of the lens elements (it's a very old lens). Here's what I get with my two fixed reversed lenses:
55mm lens (actual size is about 25mm wide):
28mm lens (actual size is about 10 mm wide):
It is more about the photographer than the camera, but you've got to be comfortable with what you're using. If you're comfortable with the older pro film cameras, you'll do well with the D90. I went from a Nikon F2 to a Coolpix 880 point and shoot, to a D40. I thought I'd adapt just fine, but I didn't realize how dependent I'd become on the Live View feature of the Coolpix, and the D40 doesn't have that. With my awful closeup vision it gave me headaches trying to frame closeup photos in the viewfinder. So I sold the D40 and was going to side-grade to the P100, but DH convinced me to do the upgrade to the D90 body and use the old lenses, and eventually I'll get a regular DX lens and a real macro lens (so buy my beads once I get my website up!). In the meantime, I am loving all the upgraded features of the D90 and have no regrets.
Then you have to work on lighting, but that's another whole topic!
-Diane