I see several reccomendations for Xeon procs, but if the only thing I am running is unRAID for pure storage, do I really need a Xeon? Probably worth mentioning that the build I am thinking of would start with 5-6 drives, but perhaps grow to as many as 20.

If it's only for storage; and you don't plan to virtualize the server,; then you don't "need" a Xeon ... but it's still a good idea to use a board that supports ECC memory.  Some of the SuperMicro boards support the Core i3's that have ECC support ... so that's a good lower-cost option for a storage-only setup.

 

... This motherboard: http://www.newegg.com/Product/Product.aspx?Item=N82E16813182820

 

... with an i3-4130, 4330, 4130T, or 4340 would be a good choice with PLENTY of "horsepower" for your server (and then some) with ECC support.