Noob Rooting question...

You are safe with the Google account as a backup but once you unlock the bootloader and reboot all your customizations will be lost (home screen, background, etc). Because of that the first thing many rooters did with the phone was unlock the bootloader.

 

Rooting the phone won't change anything on your screens or apps, you won't even be able to tell expect for the superuser app. Unlocking the bootloader will format your internal drive (everything will be gone, even the folder /sdcard, if you have flashed CWM <-- whole nother thread for this). If you are using a home screen replacement, like LauncherPro (or ADW), you can backup your home screens and restore them after a wipe (might need the pro versions). Just make sure you have the backup folder saved on your computer if you are going to unlock or lock your bootloader, as all the folders on the internal drive will be deleted (mentioned above). Your Google account just backs up your apps, wifi passwords, market apps, and some settings. If you are running the stock launcher, you can take a screenshot to help you remember how you had it setup.