few things.
I never saw a report on a continous test with something charging the system to show 40 amps to the fan.

can you send the proto type instead of getting boards made? would rather check that out before you outlay money.

The single pot is fine I think, but you probably want a 10 degree spread on the off. maybe even 15.

I have a 195 thermostate in mine, Have the fan come on at 210. Shuts off at 195, but it gets down to 189 before the fan shuts off, and it gets there pretty fast.