An airplane will fly with zero-zero thrust set-up, but they usually fly better with thrust adjustments.  Unfortunately, there is no simple answer of what the best thrust angles are, but if they suggest a certain amount on the plans, then you have a good starting point.

It is very typical to have a degree or two of right thrust, but this depends on the flying speed, prop size, and configuration of the model.  A slow biplane with lots of power with a big prop usually takes a whole bunch of thrust and incidence adjustments to perform well, while a fast clean design like a pylon racer may not. 

The common method to determine right thrust requirements is to pull the airplane into vertical flight to watch the track on a calm day.  If it just goes straight up, you have it right.  If it start pulling to the left, then you may need to add right thrust.
Check it by doing the same manouver at full power, and by chopping the throttle to idle just before pulling up.  This way you can differentiate thrust problems from rudder trim problems.

Even with the correct thrust adjustments of the engine and the rest of the airframe, you still have to fly the airplane.  What this means is it takes a touch of right rudder to do inside loops and a touch of left rudder to do outside loops so that they track.

As they say in full size - step on the ball.  There is quite easy to see the need for rudder with the increase of pitch(you pull back and the nose goes left).  The reason it happens in prop driven airplane is due to the prop blade having different angles relative to the air it is moving throught.  The downward traveling blade is at a higher angle than the upward traveling blade when the aircraft pitches up.  So (with the conventional direction of engine rotation) the right side of the prop is pulling more than the left side of the prop (if you are in the cockpit looking forward).