Before you design an arch and the pan(s) I suggest you give us more info. Most hobbyists start small then grow. How many taps do you envision in 3 years, and then in 5 years? How many days did you collect this year to get the 40 gal of sap?
I think you likely want to build something in the 2x4' up to 2x6' pan size if you are thinking more than 50-75 taps. Any of those sizes can do you well. Then if you get too much sap, consider either making an RO (many plans available on this forum) or get a bucket RO, either complete or a kit. If fewer than 50 taps, a 2x3 should be OK, then a small RO.
An RO removes more water from the sap much faster and easier than burning more wood. The right small RO will remove enough water from the sap that you can then boil 50% less volume and many will remove even more than 50%.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.