If you want to encode video, you may want to consider a i3 CPU so you can use Quicksync at some point. I haven't checked recently but don't think the Pentuim series has it.
Asrock has several motherboards with 8 Sata ports, wish I had one right now.
I bought a 400W FSP Aurum Gold power supply recently. It is very efficient and seems to work well so far in very limited use. When I bought on Newegg it was only $59.99, but after some good reviews they've jacked up the price a little bit. It has 4 sata connectors, can use molex to dual sata for more if needed. With an i3-2100, single 2.5" hard drive, 2 sticks of RAM, my old 330W Seasonics used 8W more at idle than the FSP, a newer 300W Seasonic Bronze used 3W more. FWIW I traditionally only buy Seasonic.
Comparison of systems using a Killawatt meter to measure wattage, all used the FSP setup as above, "onboard" graphics. Most CPUs were undervolted.
i3-2100 on Intel DH61WW - 18W idle (max on boot 48W)
i3-550 on Gigabyte H55M-S2H - 31W idle (max on boot 58W)
Sempron 140 unlocked (same watts with 1 or 2 cores) on Asus M4A785-M 35W idle (max on boot 48W)
Athlon 445 unlocked (same watts with 3 or 4 cores) on Asus M4A785-M 43W idle (max on boot 77W)
AMD Sempron system with one 2.5" OS drive and 5 Samsung 2TB drives with Win7 in power save mode uses 54W idle and maxes at 108W on startup.
AMD Sempron system was only about $35 for the CPU maybe $65 for the motherboard. Not all CPUs will unlock either, I just got lucky.
Another thing you might consider, although not mentioned, is getting a motherboard that supports VT-d virtualization. The VT-d CPUs are more expensive, not sure if you want one though.
My problem is software/file systems, I want a system that will run off a USB stick to conserve sata ports, but need Windows for Sagetv which will require another hard drive. I've tested Openfiler (didn't work), Freenas (required manual command configuration, menu settings didn't seem to "stick"), Nexentastor works ok using menus, kudos to them. Standard RAID or ZFS type systems will spin up all drives when writing so I am back to finding something that only spins up the drive in use grrrr, looks like either Linux with LVM and Snapraid or WHS 2011 + Drivepool + Snapraid. Might need to run 2 PCs for what I want.