OakCorner, while my evaporator is only a 2x6, perhaps my experience can give you some idea of what to expect. Mine requires about 20 gallons to flood, and yours is roughly double the capacity, so expect about 40 gallons to flood. Mine evaporates 30 gph (no air), so expect about 60 gph. Since short boils are inefficient, you will want to boil for at least 3 hours. You would require 220 gallons in your tank to start, plus enough sap to "coast" while your rig cools after the last stoke. Mine requires about 15 gallons, so you might need 30. Learn this amount and remember to stop when this much remains in the tank.
During cold periods between boils, I find that a trouble light placed under the flue pan is warm enough to prevent the flues from freezing.
At the end of the season, I prefer to "chase the sweet" by adding water to the tank when it is empty. I get a couple more draws, then call it quits for the season.
Have fun and good luck!
Leader WSE 2x6
Old metal corn crib converted to "The Shack"
2013: 100 taps, buckets, 52 gallons syrup
2012: 100 taps, buckets, 37 gallons syrup
2011: 93 taps, buckets, 47 gallons syrup