The ATI 4870 is a very new card and will certainly be able to handle your monitors. It's also highly optimized for Motion.
As far as drives, it's hard to say without knowing what your company is going to be using the system for. Not everyone needs 6TB of fibre RAID storage, but if you'll be working in HD, you should at least have some kind of RAID storage. RAID 0, as I understand it, doesn't give you media protection, it only increases access speed. Lose one drive, lose everything.
A RAID 5 in an external enclosure is probably a more sensible solution. Lot's of companies specialize in building media storage. Cal Digit is an LAFCPUG here. I've never used them, but have chatted with reps and seen their products and they look good.
Beware the D5. It doesn't shoot standard frame rates.
IMO, "pro HDV" is an oxymoron. :-)
Andy