Yeah, no issue. Did consider the stock zotac but its a blower which I assumed wouldn't be the best for cooling and noise.

What's the rule of thumb for powering the Risers? Is sata a no go?

Might just split the lot into two 6 gpu rigs...

Ditch asrock h110 for x2 ga-z270p-d3
Evga 1600w on each.
Vga 1-6 with 6+2/6 to each gpu using included gpu 6 to 8 pin adaptors.
Vga 7-9 powering x6 risers using 8pin to dual 6 pin adapters.