Hopefully simple system design questions

Well my help arrived. The way we strung the pipe in the joists was really ingenious. We fed the pipe up then down perpendicular to the joists (drilled holes), then pulled the loops down each joist cavity, feeding pex from that side. It had to be about 70-90 degrees to pull the pex down the cavity without kinking the pex. Kerosene bullet heater very helpful at -5 deg F ambient and only a tarp over the garage door.

It took two people. One person pulling and one person unrolling the pex. We got 5 runs on the far side, 6 runs on the middle and just short of 7 runs on the side closest to the manifold. We are going to splice on 15 feet approx on the closest loop to the manifold to complete the loop. A slight adjustment to flow control should fix this. 900 ft of pex ($400) 800 lin. ft of heat transfer plate ($800) 3000 Teks 1/2 inch Lath screws (non self tapping) ($100). Nice thing is, I can use leftover screws and plates for the remaining zones in the house that I have yet to do.

I figured screws would not work loose and could be removed easier (especially because im not 100% sure on plumbing placement for island with sink and other stuff. Staple the hell out of something and try to remove it and screws become suddenly worth it IMO.

The guy who is helping me felt I went way way overboard on the plates way more than he's ever seen (near 90% coverage on the underfloor) but this will help keep water temps to a minimum. He is thinking I can run one mixing valve for both both zones at 110 degrees for both the concrete garage below and the underfloor above.

I'll post some pics later.