I'm interested in pretty much the same but with ODROID C2 
I have read many threads on this forum but not found clear answers to my questions.
My general tasks for this setup are: download torrents (i have 100 Mbit internet channel), store they at 2TB external WD BOOK (with own power supply, will be formated to ext4) and then, stream this content (720p and 1080p video H264) to one client - mediaplayer MAG 250 (via samba or nfs) or Samsung Smart TV (via DLNA). All network connections will be via ethernet cable.
General questions are: what max download speed shall i be rich while downloading the torrents and will it be enough usb 2.0 transfer speed to deliver these contents to my media player ? Also these two tasks may be executed in parallel.
I understand that for example ODROID-XU4 is more faster (USB 3.0) but it have the active cooling and more bigger price. Otherwise if it much better then ODROID C2 i will buy it 
Thanks for reply.