Hi Lizard!
The rotors must rotate at different directions to overcome lift dissymmetry.
The hight difference between the two rotors is not critical, as there are no flapping hinges required. The rotor blades are just installed in a rigid manner.
Georges Chaulet (JoJo) achieved to build a flying tandem model. He only used rudder control and fore-aft-tilt of the front rotor. It seems to have been adequate.