How can I get deep sleep -> coma for max battery life as comms platform?
I think you're looking for a feature called "Doze mode" in android. Its been around since Android Marshmallow (6.0.1) . If the phone is idle the device enters in a sleep mode, pretty much what you described in your first paragraph. It suspends all the background activity and saves battery for a long time. Doze mode is enabled by default in devices running Marshmallow or higher 

 Also you can use an app called  Greenify to hibernate other third party apps that you're not using. This also saves a lot of battery for me.hope this helps

A brief description about Doze mode in android