Single Pilot
KSU Aviator is wrong...
I have over 1,000 hours in the BE-99, all of it during 135 ops and all of it alone. We had no auto pilot.
We also flew the BE-1900 single pilot with no auto pilot, but that of course required a single pilot type ride. Busy, but fun.
The old C model 99 was a great airplane, the A and B model left a little to be desired... and you are right, since it was under 12,500 lbs it did not require a type ride - just a regular old 135 IFR check ride.
You can put a guy in the right seat, but you sure don't need him. When I left the freight industry and started flying the BE-1900 for an airline (street captain), I remember being somewhat bored because I had someone sitting next to me doing most of the work!
Enjoy the 99!