Thanks to both of you for the additional info. Since I plan to stick with Windows 7 for familiarity reasons (and it'll do just fine since all it needs to do is serve up a network share, run Plex Media Server and few other apps), I figure going with a standard Asus MB is good. I like the 8 SATA ports on this, with my SSD for the OS I'll have room for 7 storage drives and that's more than enough based on my anticipated needs over the next several years.
So yeah I've got some overkill on the components, but it feels alright to allow for a little headroom down the road. The i5-4670/Z87-Pro combo with 16Gb RAM seems straightforward, and I'm now looking at the Seasonic 750W SS-750KM3 PSU since it comes with 8xSATA connectors so everything works together. Most likely going with a Fractal Design R4 case, also with 8 3.5" drive bays . I'm starting with 4x4Tb WD Red drives for storage; here's the current proposed build (<$1,600):
CPU: Intel Core i5-4670 3.4GHz Quad-Core Processor ($214.99 @ NCIX US)
Motherboard: Asus Z87-Pro ATX LGA1150 Motherboard ($167.99 @ NCIX US)
Memory: G.Skill Ares Series 16GB (2 x 8GB) DDR3-1600 Memory ($144.99 @ Newegg)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk ($79.99 @ Micro Center)
Storage: Western Digital Red 4TB 3.5" 5900RPM Internal Hard Drive ($172.99 @ Adorama)
Storage: Western Digital Red 4TB 3.5" 5900RPM Internal Hard Drive ($172.99 @ Adorama)
Storage: Western Digital Red 4TB 3.5" 5900RPM Internal Hard Drive ($172.99 @ Adorama)
Storage: Western Digital Red 4TB 3.5" 5900RPM Internal Hard Drive ($172.99 @ Adorama)
Case: Fractal Design Define R4 (Black Pearl) ATX Mid Tower Case ($99.99 @ Micro Center)
Power Supply: SeaSonic 750W 80+ Gold Certified Fully-Modular ATX Power Supply ($139.99 @ Newegg)