What is the Jukebox capacity?

Hi there,
Quick couple of questions regarding the capacity of the Jukebox. I thought it was 8gb, but I'm certain I've only copied about 4gb of music to it before it stopped copying new tracks.

Are there other limitations, like number of files/folders?

Is there a screen somewhere which will tell me how much I've used?

I've done a search in the pdf of the user guide but come up blank.
Mine is a 2013 C4 Picasso II.

Thanks,
Matt