Simply enter the respective station's position in the unit you have selected in your global settings, i.e. either inches or centimetres.
I struggle to understand your second question. You can have as many aircraft of the same type in your data base as you like, e.g. with different empty weight, fuel capacity or what ever. Just assign a different name, e.g. the tail number of the aircraft.
SkyDemon is a European product probably not known to most US pilots which form the majority here. You may want to address questions very specific to Europe and not specific to Mooney in a European f