An educated guess...
1. similar to single rotor, as lift will be shared on cioaxial.
2. Unlikely. Structural integrity will be as single rotor.
3. Yaw effectiveness will be reduced in autorotations. Flare will not suffer.
4. In theory non, but in practice only if aircraft is ubjected to reduced g - so same conditions to cause rotor strike.
5. Not especially.
6. Similar to single rotor.