Is there a limit to the number of ipods I can manage thru one copy of iTunes? Is there any difference between music I've ripped myself (outside of iTunes, standard mp3s) and music purchased thru the itunes store?
you can use an unlimited amount of devices (i.e. iPods and iPhones) with one copy of iTunes. In terms of your second question it depends on when you bought the music. Recently apple updated almost all of their music in the iTunes store so they no longer have DRM. it would be hard to say how the bit rate would differ between music you have gotten from outside the iTunes store as compared to songs you bought from the iTunes store.
According to Apple.com (emphasis mine):
When you turn on Automatic Downloads or download past purchases on an iOS device or computer, your device or computer will be associated with your Apple ID. Your Apple ID can have up to 10 devices and computers (combined) associated with it. Each computer must also be authorized using the same Apple ID. Once a device or computer is associated with your Apple ID, you cannot associate that device or computer with another Apple ID for 90 days. You can view which devices or computers are currently associated, remove unused devices or computers, and see how long before they can be associated with a different Apple ID from the Account Information page in iTunes on your computer.
Any music you have purchased through iTunes before January 2009 still had DRM to it, and will be restricted to the devices you have authorized through iTunes. Any music you have purchased through iTunes January 2009 or later does not have DRM associated with it and you can add that music to any device. As far as music that you have ripped yourself, you can add that to any device.