Tape

The drive should be formatted in FAT32 / FAT16 / FAT12. FAT32 is the most common and can be read / written from OS X and Win.
Generally not - but this is depending on the formatting. For FAT 32, the maximum size of a SINGLE file can be approx. 4 GB.
This does not apply to external HDs - only make sure that the HDs are formatted in FAT.
Basically, there is no storage size limit - but we advise to use sticks with max. 32 GB, as they have been tested successfully from us.