This is what i came up with for about 20 bucks.
(11) Box Fan Air scrubber - YouTube
I really like your design for the frame that holds everything, but I took a simpler approach. I drilled a hole in the center of each of the lower corners of the fan, and attached some 1/4x20 eye bolts with washers and nuts. Then I mounted some more eye bolts to the ceiling using plastic drywall anchors, and hung the fans upside down, with a lightweight chain, to give me easy access to the switch, but then later put them on a remote with a timer. I used short pieces of duct tape to attach a MERV 13 filter that is 2 inches thick, to the backside of the fan. Be forewarned, these filters are not inexpensive, ESPECIALLY at big box stores. No filter is going to get everything, but these do a dam good job. Amazon has the best prices I have been able to find. I have 1 of these in my shop in each of the 4 corners, and they keep the dust, mostly under control. I turn them on medium when I'm going to be cutting any lumber, and let them run for an hour on a timer, on high, after I'm finished in the shop. I replace the filters as they fade from white to a dark gray on the intake side of the filter. The nice thing about the shop furniture, jigs, and accessories that we build is that, it doesn't have to look good, but it MUST work good. The key component in your design, and mine, is the filters. The typical household furnace filter will not capture fine dust particles. By the same token, a MERV 13 filter will not work with most in home furnaces, because they restrict A LOT of air flow, and will drastically shorten the life of your furnace, unless the furnace was designed specifically for that filter. If these filters bring my 20 inch box fans to their knees, it's just $20 to get a new one. I'm not sure which filter you used in your solution, you didn't mention any specifics, but I have seen other YouTubers use filters that you could read a book through. Those see through filters are like the stop sign on the corner of my street, it just a suggestion. BTW, I subscribed to your YT channel.