How do your environmental results look historically? I don't see much benefit in running the environmental testing as a makeup, and you can further justify it if 4th quarter is clean and a history of clean results are trended.
To pile on with everyone else, a solid root cause needs to be documented to justify the corrective actions you've already decided upon. Your CA's sound reasonable, but your auditors is going to want to see that you've thoroughly checked to how it occurred to begin with. Additionally, you might want to add some verification step to this calendar you've created. Maybe at each monthly meeting a signoff to show you've reviewed which activities needed to be performed and that they were actually done. I did something similar to a couple of master sanitation schedules we had created at my old spice plant, helped us to notice "oh hey we haven't cleaned x area in the past two months, we'd better do it this month to keep it within the quarterly frequency."