Not sure where you see "remove".
When you connect the iPod to iTunes, iTunes sees the iPod and a Sync begins straight away. You don't need to do anything. Once the Sync has completed (you should see an indication of that), then click on eject - which confirms that the iPod can be safely removed (unplugged) from your computer.
It's because the Sync begins automatically and immediately that any changes you want to make are best done before connecting the iPod. There are some changes that do need to be made after the Sync has finished (and with the iPod connected). If you have to make any changes at that time, that is when you would need to click on Sync, in order for the new changes to be put onto the iPod.
There is no reason why iTunes should remove your purchased music when adding CD imports - unless...
- you are trying to Sync the CD import using a different computer to the one used for purchasing music.
- You have purchased music on your iPod Touch (directly from the Store) but you have not yet transfered those purchases to your iTunes Library, or signed into the Store on your computer. Is your iTunes Library signed into the Store?
- You delete the music from your Library.
- You untick the box next to a song's title.