usb flash or disc?

I just bought Edision Trojan. How many GB maximum should my usb flash memory be? Is there a limit?
Can I connect a usb external hard disc?
Thank you!

I bought a 250GB external usb hard disc, but had some problems: After I formated it to FAT32 (the whole disk), I connected it to Edision Trojan and it didn't recognise it. Then I formated only 31GB, connected it to Edision and eveything was OK, except I used only 31Gb of the 250. Any solution?