@johnny2678 just in case you didn’t see @timber’s reply above, the Rachio 3 is compatible with the Generation 2 outdoor enclosure.
We estimate 2 years. Battery status will be displayed in the Rachio app with reminders to change 
TBD
1 inch
The flow meter should be installed on the main line. Using time stamps from the controller, we can connect individual zone runs and usage in the cloud.
No, the long range radio is required to communicate with the Rachio wireless flow meter.
Interesting use case and good question. We’ll need to design a configuration for this.
We recommend installing on pipes 1 inch in diameter or smaller. Accuracy will be reduced installing on larger pipes.
After the backflow. The flow meter would be installed within the 18" section of straight pipe. We’ll post more visuals soon.