I've used a lot of Jim Kendrick's dew prevention gear on my scopes - it works well. http://www.kendrickastro.com
In lenses, apertures, ISO... The short version is that you need to experiment with your camera. I strongly recommend stopping your lens down at least 1 stop. I do not recommend a zoom because sometimes the focal length changes and things get weird. This is not a bad thing - simple primes can do a very good job.
The 500 / focal length rule is ok - it may be a little conservative. Pixel size is important but the sensor size is is irrelevant. This means that if you have ~6 micron pixels - like the 40D and 5D2, the motion blur will be essentially the same.
Bear in mind that it is easy to construct and use the most basic of tracking mounts, the barn door tracker. There are many designs on the web, some are complex while others are trivial. For those inclined to buy a tracking mount, Astrotrac and Losmandy offer ready bought solutions.