Unless your files are on floppy disk, I'd avoid the tyros 1 (no USB A port); earliest that had this was the PSR3000, *but* your flash drive must be FAT16, *not* FAT32 (which is default on most USB sticks); FAT16 maxed out at 2GB, btw, so that even if your usb stick were larger than 2GB, once formatted, that's all you would have.
You could of course, upgrade a PSR3000 to FAT32, but you'd need a smart media card reader/writer to do so (and a smart media card, harder to procure than a floppy disk at this point).
So I'm telling you Tyros 2 or later (T3/T4/T5/Genos, s910/s710/s950/s750/sx700/sx900; ironically the sx600 does not have full midi editing capabilities .
Yes if you find a working s900/s700 that would technically work, but I'd avoid those different reasons.
If your song file *is* on floppy disk, then by all means use a PSR2000/2100/1500/1100/1000 or the even older PSR9000/8000, Tyros predecessors
Mark