I meant upsizing the coop and run.Upsizing past 6 birds would require legislation change, so I'm not going to hold my breath. (It's probably a good thing to keep me from getting too invested in chicken math anyway.)

The enclosed portion of the coop has a hardware cloth window of 6" x 6' opening into the run and the sides each have the angled bit that tapers to the end of the roof. I had originally also included another 6" x 6' window on the back, but all the books kept harping on NO DRAFTS and I got nervous and covered it with plywood in the design. I could easily add that back in and add more to the interior wall. And I can make them with removable panels without too much fuss I think.
Is there a rough percentage of open-to-solid I should be going for on the walls while avoiding the dreaded drafts?
The top vents you have planned are great, and would likely be enough in moderate temperatures, but hot summers would definitely favor more ventilation, like 2-3 sq ft or more per bird vs 1 sq ft in moderate climates.
Drafts may not be an issue you ever really need to worry about. In the summer for sure your birds will appreciate a cross breeze over the roosts, which is why I suggested a removable or top hinged panel that could be propped open for more air flow. During colder weather or windy, stormy weather, you can close them up most of the way to keep the inside of the coop dry. Example of a coop w/ top hinge panels: https://www.backyardchickens.com/threads/coop-ventilation.1452812/page-2#post-24868607