That's my usage of n770 as I said before. I use arm compiled aria2c application - very light and not so resources extensive as ctorrent.
Although I'm not using external hdd - i use internal card with ext2 filesystem (I've had problems with fat).
I've set up usb-host permanently so I can connect any pendrive from powered-hub.
I tried to power tablet itself by hub's supply but spikes caused by the charging process caused drops in hub's and connected stick voltage that were too much for them.
Disadvantage is to have combined power supply - one for charging, second for powering usb devices.
My electricity bills dropped drastically when I shut down my PIII working as home server and replace it with linksys wireless router in combination with n770 working as torrent downloader.