i would think a 2x6 is ideal for you. you can add a preheater in the fiture if you expand. the problem with starting with a bigger evap is that you need a lot sap to fire the thing and then get the hang of the new set up. a 2x6 with blower and good pre-heater can probably do 40-45 gph. if you had 250-300 taps you could go with bigger one but would still need a good 2 day run to really get it going.