There was a good article by George Hicks in a recent magazine, 3D Flyer maybe, I forget about the need or not for right thrust. The airplane has a natural left yaw because of the spiral slipstream and as a compromise moment balance the right thrust is used. The vertical heights of the aft fuselage and kind and area location of the vertical tail will give different yaw effects and so need different amounts of right thrust.

You can start with zero but be sure and keep the speed up and be ready to correct any yaw or roll that would be a problem (as if you would be sound asleep on a first test flight!) It is hard to go too bad with a couple of degrees. On most of my normal configuration models I have to admit I just eyeball in a touch of right thrust, mainly to be sure it isn't left thrust. On a high quality aerobatic machine a more precision approach will be needed.