How low was the oil level?
The engine oil will be fine as long as it's motorcycle oil, and it's safe for use with wet clutch's
Air filter should be fine as long as it was cleaned before oiling it.
Find out how many turn's out the mixture screw is currently set at.
I reckon you might want to adjust the valve's, and then adjust the carby to suit
When it cut's out did you remove the spark plug then earth the spark plug threads on the engine and try kicking it over while looking for a spark?
What colour is the porcelain on the insulator of the spark plug when you pull it out?
It could be one a few thing's, maybe stator, cdi, ignition coil, fuel problem...