Not sure if there is a standard level that people use, but I run about 1" over the flues and about 1 1/2" in my syrup pan. Since it's your first boil, you'd probably want to start deeper (like 2" in each) and bring up fire temps slowly to make sure everything is solid before cranking it up. The rear float will probably need to be adjusted towards the end of the boil as the sap in the head tank gets low (less pressure on the inlet).