Castles are militarily useless; have been since the advent of artillery. Building a house so that it's hard for people without heavy weapons to attack is easier, and can be done using green architecture, as well. Build into the side of a ridge, for example.

The growing-range for wheat is predicted to move into canada; there are sections of the US that would become more suitable for crops such as amaranth and quinoa. This'd take some rather detailed recon work; farming suitability is also related to who's been using which pesticides where for the last century or so.

I'm not thinking that far ahead ATM; if I were, I might be looking at staying in a port and getting a boat to live on.

best,

Joel