1. Is there a way to test the sonar in mission planner - i can't tell whether it's working or not
2. my yaw stick seems to be set correctly - right to arm - but the actual yaw motion of the quad seems to be reversed - the other channels are all ok. Is there a way to sort this out?
The CLI has a test for Sonar.
Yaw right should be high PWM. Check your props and cables are in the correct order.