Both of your Ipods should work fine. I know it seems like Apple is leaving the original ipod brand behind, but the classic is still the most recent release and still supported by itunes! Shouldn't matter what computer you upgrade to.
You shouldn't lose anything when you sync the ipod, but if you want to transfer videos off of the ipod, you may want to try to select the option to manage your ipod as a hard drive. Then you can probably copy it over. If that doesn't work for some reason, a third-party app, such as YamiPod and Floola. They both can also be run directly from your iPod in disk mode so you don't have to install any software on the computer your using.
Purchased videos, however, can be transferred by selecting "Transfer Purchases" on the ipod.
A more direct approach requires you to go into the ipod directly. I've only done this on windows before, and I found the videos I wanted in the \iPod_Control\Music.
Hope that helps.