For the Mobo I suggest finding a decent board (AMD based one if you want ECC RAM) and then use a PCI-e controller card to support the hard drives you need. It is hard to find a nice MB with all the SATA ports you need, using an external card gives you a lot more options. When I researched it everyone recommended an "LSI Logic Controller Card LSI00301 SAS 9207-8i" (eg. https://www.amazon.com/LSI-Controller-LSI00301-9207-8i-Inter...) and it has performed very well for me. If you go that way you'll need a SAS to SATA cable, they are easy to find as well.
For the Mobo I suggest finding a decent board (AMD based one if you want ECC RAM) and then use a PCI-e controller card to support the hard drives you need. It is hard to find a nice MB with all the SATA ports you need, using an external card gives you a lot more options. When I researched it everyone recommended an "LSI Logic Controller Card LSI00301 SAS 9207-8i" (eg. https://www.amazon.com/LSI-Controller-LSI00301-9207-8i-Inter...) and it has performed very well for me. If you go that way you'll need a SAS to SATA cable, they are easy to find as well.