Did you look at
Home Climate Control
at all for the software end of things?
It's algorithms and design look pretty good, and I'm planning on extending it for my system:
Gas heated multi-zone - 2 zones with UFH concrete slab, 2 zones with hard wood, and 2 zones with ceramic tiles plus 3 zones with "radiators". I also plan to have summer cooling with an outdoor underground cooling loop (no heat pump).
Should be reasonable to get the software up and running on a pi or similar.
Did you look at i2c to 1w bus bridges?
Cheers,
Tim.