Ideally what you want is that your fans are on 18 or 24 hours a day and they keep the temp in check. Using a thermostat promotes heat spikes and fluctuation (Bad). You do want a day/night fluctuation of less than 10 degrees. And you always want it cooler at night

You should always have a stronger exhaust it creates a negative pressure (suction) so your filter will work better. You will also move more air through the room.

Think about it this way. 225 and 400 CFM. Remember these are MAX CFM not actual. I don’t know what your actually getting. So if you have 400 intake and 225 exhaust, the 225 is probably moving close to its max (say 220) because your room is under a positive pressure (it’s pressure is slightly above atmospheric pressure). So you have both the pressure and the fan pushing air out of the room.
If you place the 400 as exhaust and 255 intake you wont get 400, but you’ll be getting a lot more air through than if you had passive intake.
With a stronger exhaust you wont have air leaks, and thus smell leaks (if it’s a problem)

You might want to consider having the 400 on all the time (or at least while lights are on.) and the 225 on the thermostat. So if the temp starts to get too high 82, the intake’ll kick in and increase flow--> decrease temp.

?? How accurate is your thermostat? Can you set it to keep the room within 5 degrees? Between 77-82 that would be best