transfer iTunes to new iPod

Don't worry about the old iPod. Assuming that all your music is in your iTunes Library, all you need to do is connect the new iPod to your computer and when iTunes sees it, set Sync options for that iPod. (Using iTunes, look on the Device/Settings/Music pane and set the Sync options that you want.)

Each iPod is set up as a separate device so the setting for one can be completely different to another one. You can add different music to each iPod. For example, if you want only some of the music in your library on the new iPod, set the Sync Music button and then select the next option to Selected playlists, artists, albums and genres; then choose only the items that you want to add to the iPod.

That's a brief explanation, if you require more assistance, please check out the following Apple article; Sync your iPhone, iPad, or iPod using your computer - Apple Support or ask here.

Note that while each iPod will have its own selection, some things will affect both iPods. For example, the Play Count, Last Played and Smart Playlists will all be affected by both iPods. For example, if you change the rating of a song on one iPod, it will affect that rating on the other one too.