I have a system with a similar build to this!
Main Unit - Lenovo Thinkserver RD650 (70D00025UX)
Attached Storage - ThinkServer SA120 (no model number on me, sorry)
RAID Card - LSI9280-8e 6Gb SAS RAID
Extra CPU - Intel Xeon E5-2630 v3 (8-core)
Extra Memory - 3x 8GB stick, 16GB storage for each
Operating System - Windows Server 2012 R2
Hard Drives - 6TB WD Se drives, SATA for the main unit, 4TB SAS for the DAS
Multiple servers can be used to decrease some costs, but this will give you a good handle on the build.
Luxriot also builds their own servers if you live in the US. The warranty seems to be reasonable.