Sorry, I didn't read thru the whole thread, but a several things to consider: fire blocking foam is not the same as insulating foam. I have read that there can be issues with foam on metal and corrosion, and the fumes from burning are deadly. Some research is in order before you buy any foam. It's pricey, but in projects I have been involved in, it sure insulates/seals well. And like MNBobcat said, you are probably going to find it is cost effective for a large installation to have a commercial installer do it.
For best bang for your buck, I would be sure to put at least 4" of rigid foam board under your floor slab at the perimeters, and 2" under the rest of the slab. You can work in 50 degree air, but cold feet are a problem.