Let's see:
Rotor stall - I'm not aware of any helicopters that have a significant rotor stall issue in the normal operating range of airspeed and Rotor RPM. Why is there such an interest for a co-axial?
Who teaches rotor stall on Bell 206? I've never heard of it being an issue, except perhaps for very high weight/ high density altitude, low rotor RPM autorotations...
AUtorotations for co-axial rotors with mechanical flight control systems are a problem because of the way yaw control is mechanized. What works in the proper direction in powered flight for yaw is reversed in autorotation. So all the current co-axial machines use large vertical stabilizers and rudders and need to have forward airspeed to keep yaw working the 'normal' way. The KA-32 Flight Manual has a minimum airspeed in autorotation of about 60 KIAS if memory serves me well. Below this airspeed 'Special Techniques' are necessary. Flare and landing shouldn't have much yaw corrections needed, and the landing certainly would not be 3G.
Risk of coliision of the two rotor systems is minimized by the large vertical separation - the worst case is high speed and I believe pulling G. Happened to one of the KA-50 prototypes, I understand. But not a problem in the KA-32.
As far as maneuverability, I don't believe co-axials have any particular advantage or disadvantage - Nick Lappos would elaborate.
Vortex Ring State symptoms and recovery should be the same as single rotor.