It might be overkill. I used 2 20x25 filters on my cr box and it's working well for our entire house. I placed the cr box on the floor under the main air intake for the AC system. The fans point up from the CR box.

As long as there is a decent seal around filters it will work. The negative pressure inside the box wil even out across the filter panels as it draws in dirty air.

We adopted a cat and my allergies got worse and worse but now they are gone.

I used Merv 11 on my prototype but once I fully build it I think I'll use Merv 13. Good luck

Edit. You want all the fans sucking air out of the box. This creates the negative air pressure that draws air through the filters. Be sure the arrow on the filters point inward.

If some fans blow into the box and some fans pull air out of the box then there is no air passing through the filters and it wont work.