My opinion:
For a personal use helo the first consideration in configuration and rotor size is that it have good autorotation. Cruise is secondary.
Putting another rotor above the other only increases downflow and therefor is not as good for autorotation.
Coaxial has some advantages for easier to hover. But a large single rotor should be somewhat slow in reacting as well.
Just a friendly reminder, try searching this forum for extensive discussion on this topic.
regards
slowrotor