I believe that I did a post on this, so I do not feel like repeating the knowledge again, look at my past posts, but the bottom line for underfloor radiant heating is do it right or do not do it. You must use the metal plates, and the best way for insulation is rigid cut press fit and poly foam the cracks, I posted pics of this. Also glue/slilcone rtv and screw the plate on, rtv has a better conduction rate that air.
And Yes, use a mixing valve, 300 foot max tube length for zone. The controls are up to you, hint, I kept it real simple , kept my money in my pocket and it works great. You do not need to buy the hype. But you do need to do it correctly. Want to save $, build your own manifolds. I have seen drs/lawyers throw all kinds of $$$ at poorly designed systems that have all the bells and whistles , but the design from the start was bs, and will never work, poorly at best. Spent $30,000 for a system that they spend twice the money to operate a year, than the system that was replaced, and the funny part is, they are happy with it, for the past ten years.
Oh, and there is a ton of info out there on this, you just scratched the tip of the ice burg. builditsolar.com has a good underfloor radiant heat section/forum. good luck!! r