I am not a licensed electrician. I have however completely wired 5 homes with permits and passed per WA labor and industries. With that I am comfortable doing the following.

I am now building my home, 2 stories with attached garage with a mother in law APT above garage. I am having trouble understanding (or finding the proper code) how to run power for everything.

My Plan:
320 Amp service on outside wall of garage. From there 2-200 amp circuit boxes. One 200 amp (box A) installed 30 to 40 ‘away inside garage wall common to house. Wire would run in ceiling of garage down wall common with house (this would save me allot of wire for each circuit) Second 200 amp (box B) would be installed outside wall of garage (but inside). From there it would power a 100 amp (box C) circuit box inside mother in laws APT. Rest of space for future detached garage. Hope this makes sense.

My question
320 amp meter panel with 320 breaker would that be code to kill power to whole house in case of short?
Box A is 30 to 40’ away from meter. Will a 200 amp breaker at the box be code for a short or do I need to install main disconnect box next to meter because of distance or will a 320 breaker be OK?
Would box B need a main disconnect box or will a 200 amp breaker be code?

Too many questions for a sight unseen commentary...
If you are not knowledgeable about the code requirements for service installations, I would strongly recommend a licensed professional to assist or guide your efforts "on site"...
Electricity is inherently not a safe subject and you cannot depend on some plan review or "walk through" inspection to verify if something is done safely...