How much storage are you exactly needing?
Installing several drives in an enclosure and making them "one drive" is called RAID 0. There are some major things to consider for RAID 0. Google it to get some more info.
I own a couple of different media storage drives. One is a firewire 400-attached 2 x 1tb (2tb RAID 0) that has been running just fine for three years or so. The other large drive I use is a NAS (one of the Western Digital ones) that is a 2 x 1tb (2tb RAID 0) that is attached to my router. This runs all the time, has sleep mode, and does quite well. It has been going great for almost two years.
The media I have on the attached drive is roughly 500 DVD rips.
My NAS backs all that up (for the time being).
To be honest with you, you are going to have to have an insanely fast network connection in order to share BR rips to your Popcorn Hour over a wired ethernet connection.
Really, my best advice would be to start with a small drive and see how this works for you in your setup. Test it all out to see how it will work in the grand scheme of things, especially before you go out and spend 500-600 dollars on building yourself an 8tb array, which is possible.