"Either way you do it, you have the option of
installing Fedora as a non-destructive upgrade, so if you already
have files on a USB drive you can keep them while still turning the
stick into a bootable drive. In practice, however, I found that I
got better results by zapping the stick's files and reformatting
it. After all, it is just a USB drive. As far as I'm concerned,
they're meant for temporary storage.
"I also found, although Red Hat staffers told me that you can
deploy Fedora on USB sticks with as little as 64MB of storage, you
really don't want to do it with drives that hold less than 512MB.
Officially, Fedora recommends that you use 1GB or larger USB