You journey sounds so exciting!
When it comes to cooling, look up what they do in hot northern Australia (zone 1)
Avoid Solar Gain:
Roof:
Shade Sail, green roof, reflective metal/white roof, R-40 insulation
Walls: white paint, shaded by trees/cloth/etc, living wall, roof overhang, earth bermed
Windows: roof overhang, awning/etc, low-e glass, place most windows on the north or east side
Floor: Earth Coupled or blocked crawl space, shaded ground, pex pumping with cool water.
Avoid Heat sources:
Kitchen: Try cooking outside, maybe bake less often, soak things to reduce the cooking time, eat more raw food, etc
Bathroom: take cold shower vs hot, reduce humidity by using a rag, run the water less, take a mini bath
Laundry: Try sun dry, or keep the appliances outside, wash with cold water vs hot water
Appliance: Use a 20W laptop vs a 1000W gaming computer to read the news
Release Heat:
Floor: mop the floor with cold water, pex piping pumping cool water
Bathroom: vent the humid/hot shower to the outside vs inside the house
Kitchen: Vent the hot, steamy fish smell outside before it fill the house
Ventilation: prevailing wind, wind trap vs wind break, cross ventilation, ceiling fans to cool humans, whole house fan/vents
As for the stem wall. I recommend earthbags filled with gravel/stone/sand.