Looks pretty awesome, that is the sort of thing I would love to do. I am not a huge fan of predator tanks, so I would likely make the reef tank bigger (especially wider 4 foot width is awesome in reef tanks)
I would make the predator tank not so deep, keep the footprint, and make it into a reef. I would then make the reef tank deeper and have it the predator tank.
I am not sure if you are looking for suggestions, but I have a few more.
Width in a predator tank is overated IMO. Of course it depends what you want in there. I large grouper might need the space. I can just see the triggers hiding now.
A geothermal system sounds awesome, the best choice. I would have a dedicated HRV for the fish room though. You could have a couple of inputs for the HRV that suck air from a custom hood built over the tanks kind of like a stove hood in the kitchen.
Keep us updated, and remember the pics.