If you're worried about choosing an oil viscosity, take a look at what the experts have to say..
Oil Types, Weights & Viscosity FAQ - ValvolineĀ®
As others have mentioned, it is prudent to use the same oil as used in the main engine. There is no problem using an oil that achieves a higher standard than called for, but the weight should meet the manufacturer's specifications in terms of weight versus anticipated operating temperature.
As the PM schedule permits, I switch the oil and coolant over to that used in the main engine to reduce the amount of spare fluids carried onboard.
That is what works for me,
-Matt