this job is about a #2 on skill level, but a #10 on prep level. The room should have been tented off, and everything tarped or removed that could become HIT with the stuff.
Have you tried removing the screens from the window area and gently sprayed them with water while flat on a surface? This stuff will come off pretty easily but you could also ruin the screens, although fiber is very strong.
Before I resolved to re screening, I would take all screens to the car wash, lay each one flat on the drive and braced against a wall or they will go flying. Then carefully gauge the distance from the screen and let the soap and water run.
Keep that wand about 12 inches from the screens and slowly come in or out to see the progress at each distance.