I'll be interested to hear what the expert says when he visits. I met a guy online who is a premiere installer for Arctic Hydronic Heating and his company is about an hour and a half away in Missoula. Arctic systems both heat and cool but their heat pump stops working at -22 degrees. The house has electric baseboard heaters currently, and he may recommend keeping them as a backup. Also, since we are gutting so much of the house, he may recommend ceiling or walls over floors due to some benefits when cooling - I just don't know. Also, I will want to install an ERV system since they are generally recommended and we have radon levels which are within limits but still pretty high.
For the basement apartment, I bet he recommends a minisplit down there rather than using radiant heat. As far as warmboards go, we won't be using it as a subfloor but they and some other manufacturers have systems that sit above an existing subfloor. So, we will end up going with one of those systems. I know we aren't going to pour gypcrete for a bunch of reasons.