Just on the 32GB USB card. I suggest a smaller size ie 8GB or 16GB (for the FP)
I am using an 8GB - there have been some postings on issues with the large size ones ie 32 or 32+ depending on brand etc..
Also , and as others have posted , whilst you may store all your stuff on the USP as a backup etc , the USB that the PI will use (or SD card /USB on the BBB) is dedicated to that player.
It needs to be formatted before use as FAT32 and then the FP will use it to create directories, load stuff, write logs to .
In addition you need to use the FP file manger to upload to that device as it will accordingly arrange stuff depending on whether the item is an mp3 , fseq , script etc into different areas.