Partial Answers from this ReadyNAS FAQ:
What file system should I use on my USB drive? Since NTFS support is Read-only (Note: RAIDiator v4 firmware allows write access to NTFS file systems), you can use either Ext3 or FAT32. Ext3 allows for better retention of file ownership and permission and may be more appropriate in a mult-user backup environment.
Can I attach a USB 2.0 Hub to ReadyNAS USB Port? Yes. But please pay attention on power if your hub is bus powered.