Back to your second question... yes, added cooling will be needed. There is a bottom front case cooling fan that you may already have. There is a unique very bottom flat long dual fan cooling device for the PCIe slots area from below. I'll include a picture of the Z4 G5 case bottom so you can see the new perforations down there to allow good air flow through the bottom flat dual fan cooling device, and also a pic of the left side case cover with its new perforations there too:
A good HP PDF to have:
The bottom flat dual fan cooling device which is not really a PCIe retaining device. It actually lays flat over the bottom case perforations and pulls in cooling air from below. The side case cover perforations provide the preferential venting direction: