When you're ready to shut down just flick the switch. Paint to thinner ratio or Viscosity is the amount of paint put in as opposed to the amount of thinner. I haven't had to use a viscosity cup yet for modeling. Fortunately, the best vendors let you know how much the paint should be thinned. Just pour, or use a large pipette to transfer the liquid to your jar and you're set.
Pipettes are excellent for moving liquids.
If you have some of the large ones, hang on to them. Spraying position or Proximity is just the way you hold and spray the airbrush. You should have a firm grip and a loose attitude. Get over the first time jitters by pulling out the cardboard and practicing. Basically, you should work with the gun and you in a comfortable position.