Since you mentioned you did this in the past, I thought you had experience.
Depending on the selected region, voice package can have multiple languages.
Since you only need Spanish, there’s a smaller voice package that contains Spanish among other few languages thus reducing its footprint. The package name is the one I’ve sent before.
Gracenotes is just artwork for the media player if the reproduced media has not some art embebed in its metadata.
The installation of GN is not mandatory and up to user’s preference.
Based on my preferences, I would install GN by installing a smaller voice package.
You can get some guidance in installing a voice package in this thread → Tutorial: Sync 3.4 NON-NAV APIM: Failure to Update to Newer Version Sync 3.4
You just need to download the package I mentioned before, create the USB as per the guide and run it against the unit.
Once you do, re-create the interrogator log to check how much free space you have.
Depending on how much free space the unit has, you may or may not be able to install GN.
Which GN package did you try to install?.