Prop mounting should suit your preference. Right handed people like the 2 o'clock position best. With the carby at the back of the engine, prop b;ade wash will not influence carb function, so the position will have no influence on motor running.
The red dot you refer to is the ignition pickup magnet. The other is green to indicate reversed polarity. 3W has a two-magnet system, like most electronic ignitions nowadays.