I can tell you from experience that flying single pilot is not as safe as flying with two, I think that everyone knows that. However, many factors dictate the safety of single pilot ops. I have flown thousands of hours in both single, and dual pilot ops. I used to fly a King Air single pilot and can honestly say that it is one of the best planes that you could fly single pilot.
One thing to keep in mind is the type of experience that the pilot you plan to use has. I had been flying C-402's for a thousand hours, single pilot, w/no autopilot or really anything helpfull. Therefore, I had lots of single pilot IFR time and found the King Air pretty easy to fly. Everyone pilot at the company had the same background with extensive single pilot IFR background before being hired into the King Air. What i am saying is, having enough flight time is one thing, however, if you have never done that type of flying before, you would be in for a rude awakening.
My opinion?
Someone with a good single pilot background could do the job well if that is the direction that you decide to go. Now, with that being said, I would not operate it with only one pilot. I found myself in many situations when having another pilot (even if it was a low-time guy, such as pulling out charts to a diversion airport when hand flying in moderate turbulence and IMC) would have really helped out.
I feel that from my experience, two pilots would be a much better way to go, however, if you absolutely want to do it with one, it can be done.