What ext. wall assembly is recommend for a timber frame house (heavy timber)?
The building will be in U.S. climate zone 4. 60 inches of annual rain. Hot and very dry summers. Since it is wildfire prone, fire resistance is needed. Simple gable roofline with minimal eaves. Rect floorplan, slab on grade aligned on east west axis.
Being a timber frame home means you have a lot of options for insulating since the load is already being carried by the posts. So you can go with a number of wall assemblies, but if fire prevention is your concern, I would be looking at things like Metal or stone siding, anything non-combustible. As for insulation, I would suggest maybe Rockwool (mineral wool) insulation as it is spun from stone dust and is fire proof.
Here is our page on Choosing Insulation which will give you many options, and here you can check out Rockwool Insulation and this page here is about Choosing Exteior Siding and Cladding.