Another consideration is the 2000 audio file limit of the internal Music database and a separate 2000 audio file limit of the external music database. You may start to experience this OS limitation at 12 - 13 gb on the micro SD card.
You can play around with m3u playlists to overcome this limitation. You should design playlists using audio files already stored on the internal or micro SD card. Playlists can reside in their correspinding subdirectories under Music.
If you decide to try using a 32 gb micro SD card, you could decide to read more about Playlists and Folder Mode within the dozens of messages about these topics in the SanDisk Forum.
