Yeah, you are right, there are "only" 6 PCIe slots on the board.
So one question is still unanswered if I'm correct: do I have to plug into the MB the two 12V PCIe connectors or is the power enough what the riser gets from the PSU? (and the 8PIN EVGA additionally into the GPU)
Why is monitoring the power draw necessary? Can I do something about it to reduce?
It sould be enough if you power only your riser card and vga with pci-e. I remember some previuos gen mobo had that molex connector for "extra" power too.
PCIE_12V_1/2 (PCIe power Connectors)
The power connectors provide auxiliary power to the onboard PCI Express slots. Connect the connectors depending on your system requirements.