1) Yes there is and I've done it. What I did was let the receiver format the new drive, boot up Linux, attach both drives at once, and dragged/dropped the individual program folders from one DishArc folder to the other. It is most convenient to boot up a version of Linux that allows you to log in as root, to avoid having to "chown" all the files to get it to work right. (The files must be owned by root.)
2) Of course! There is no issue there. Many customers have multiple EHDs; I've heard of some that use TEN.
3) A USB hub will work, but only if one drive is powered at a time. The 722 will not acknowledge more than one drive attached at a time. (More than one are possible on the 922 and Hopper, but that's not our case here.)