Can I run 4 USB flash drives off of my B+?

Hi it seems like the cheapest solution to get local music through my Volumio B+ pi would be to just put 4 USB flash drives on it containing my music.

My pi also has an audioIQ DAC/AMP on it

Is this possible?

What is the directory structure of the music that should be on the flash drives?

Should be also working with 4 USB sticks