1. I don't know this answer. Good question.
2. Although I'm not completely clear on your question, generally the answer is yes, you can Import individual songs from USB C or A.
However, the USB disk MUST be formatted as FAT32. And the songs must reside in a folder structure that the B2 can deal with.
music\ArtistName\AlbumName\tracks
You can have as many song tracks as you want, or as few. You can name the Artist folder whatever you want, and same with the Album folder.
The names cannot exceed 170 characters, but mostly that's not a concern.