My faborite dust protection is made by Rockler. It's a battery powered respirator. Fairly light and very soft on the face and mine blows a bit of air out the cheek area, which keeps my glasses from fogging. See pix.
Cutting your own sheets to size from a 4x4 sheet only requires a circular saw with a decent blade, and a straight edge to guide it. If you're not doing much else with it, you can buy a used saw for less than $50, new for double that. For a straight edge, you can use the edge of a large sheet of either ply or mdf, although the mdf will be more fragile. My DeWalt 18v saw easily handles this kind of cut and there's no cord to manage. Pix shows a fancy version that adds a piece of masonite, which will hold up for many years. Make the masonite section wider than the offset of the saw's blade and cut it off. That gives you an edge you can set right to your cut marks and helps control ragged edges, tear out. This will work for most of your cutting to size. Buy a 2 inch thick piece of insulating foam to lay your mdf on when cutting. Cut it outside on your driveway to let the sawdust blow away.
Finding a piece of really straight 1x4 to guide the saw may take going through dozens of pieces at Home Depot. After a rough sort by sighting along the edges from the end, I lay the candidates on the concrete floor, which is usually quite flat. I check all four sides to see if they really lay flat. That reveals twists and other flaws. If you find a really straight piece, count yourself lucky, and assemble your guide quickly while it's flat.
Hope this is helpful. Sounds like you really enjoy using your CNC, so I've attached a pdf of suggestions for making money by marketing your output.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 05-17-2019 at 12:14 PM.