I am not happy with the vast amount of heat bridging into the walls and would like to --at least insulate the metal joists to the concrete or bricks. Alternatively, IF it was available in Chiang Mai, it might be possible to use ACC blocks in the last row of the wall structure. As to the posts in concrete and metal, I would like to put some wood there too. Any thoughts?

You run risks of termites etc., potentially also fire using wood, better to use QCON or similar - if a gap exists between the steel and the walls, try inserting insulation to prevent radiant heat and conductive transfer.

Bad idea.  The heat in the walls is coming from the sun and ambient temperature.  Should not be a problem if you have AAC walls.  If not, grow trees, paint with top grade, put reflective bats in your attic are other options.

Yes and no! If external walls then sure, but internal walls suffer from heat bridging as a result of the walls being built right up to the steel. I presumed the OP is talking about internal walls primarily.

Personally if I was to build another house here I would go with double brick AAC for the heat & also for electrical installation 

Also making sure the electrics in the ceiling are in conduit & junction boxes allowing for Insulation 

& having the foil under a tin roof ( they cool down during night ) not like tiles where they stay hot 

& Making sure your roof is Vented big time 

Then you only have to worry about some awnings or verandahs along with the gardens