The Orbi is passivly cooled and having a "tower" provides a chimney effect and when I put my had over top its rather cool. I would say you could mount is upside down but I don't know how you would do that since there are no keyholes or anything on the base of the unit. Also you need to think of how the antenna arrays are configured. You may not get optimal wifi mounting it that way.
One the power it's only though the power adapter there is no option for power over ethernet or useing ethernet as a backhaul.
