Replace many USB drives with a RAID5 array

I'm looking to store recorded video on a raid5 array. Performance not a big issue. But I need to configure 6-10TB. I was thinking 5 x 2TB drives in a raid5 array to get 8TB usable.

If I build a server with i3-2100, MB, case that holds 6 drives, can I get a MB with support for a boot drive, optical and 5X sata array = 7 sata ports or do I need an add in card? Don't care sata 2 vs. sata 3.

Am I better off with an external enclosure with the 5X drives attached to a raid card in the PC?

PC is currently an older AMD 5000+ with TV capture card writing to many USB attached HDDs. Thinking to replace the PC because the MB only has one PCIe slot, rest are PCI and the case does not have enough drive bays. Building a PC to hold drives seems similar cost to buying HW raid enclosure ?

Suggestions ?
 
I ended up buying a Sans Digital TR5UT + B raid enclosure with 5 X Samsung F4 2TB drives in raid5. Setup was pretty easy. Am in the middle of full format of 8TB @ 100Mb/sec. Should take a day. Cost was $500 for drives and $270 for raid box from newegg.

forgot: also swapped server to q6600 based system on G33 chipset that had a free pcie x1 slot for the bundled eSata 6gbit card. The PCIe x1 slot is only gen1.1, but 250 mb/sec should be plenty of bandwidth for this setup.