Ripping dvd's to hard drive

Yes, you can add external drives to the hub for more storage. The limit per external device is 2TB. One thing to consider is that APPLE TV’s limit is 720p. You cannot get 1080p quality. On the hub it plays 1080p movies great. 

I would use DVDdecrypter to rip my movies into ISOs. That is what I use for my DVDs.