I to am doing my first "flying stabilizers". I have found the below charts to be very reliable.

1 kg should do very well. These surfaces SHOULD be balanced pretty close to a neutral load condition. Mine are. I checked them out with a LARGE high speed exhaust fan at a factory with a wind guage. I am using HS-55's . No joke. I did my own support system.

Do MILD dives at steeper & steeper angles to prove out your servos can do the job. Do not get carried away with the steep dives. Plane was not designed for them.