I did one similar last summer.
As said earlier, remove all the secondary double glazing and make sure you know which panes came from which windows.
When cleaning, make sure you have plenty of old cloths or towels to soak up all the dirty water or you'll be making stains on carpets or wooden floors.
If you are leaning them against internal walls to clean, make sure you have protection at the point of contact, you'll either damage the wallpaper or scuff the paint.
It took us around 22 man hours to do 72 large windows, both sides of secondary units and inside and out of main windows. They were absolutely plastered in fly poop and dead flies everywhere.
Good luck