how much oil in the pan?
 

so with an engine running what is the safest amount left in pan when checking level.?is there a rule of thumb when gauging the dipstick to ensure your not too high or too low?with the addition of external sumps and coolers and line capacities how do you ensure the right amount of oil is in motor?

I believe if you are running a prescribed dip stick you should be good as far as level. Since the dipstick is in relation to the block and pickup.

Seems to me that if you get the oil hot enough your oil thermostat should open up and let oil into the cooler. Once the lines and cooler are filled then have the oil capacity in the pan that is required for said pan. No need to run the engine to check oil level. 6 quart pan = 6 quarts of oil in the pan with engine off.