August 27th, 2014 04:05 PM
HDD won't matter. SSD might if you want to go with the M.2 (NGFF), especially if the board is PCIe x4 connected and you can get a M.2 SSD that is also X4, like the Samsung XP941.
Case - only matterd if you buy one too small for the board you eventually buy.
PSU - size it for a high end board, 6 HDDs and 2 high end GPUs and it will be plenty...