Ok... 100 magnets on the way. 8 per window / 10 windows.
I measured the area available for installation behind the aluminum frames and to sit flush you basically have to stay around 10mm wide and a max of 2mm thick. I ended up getting 1mm thick.
Here is a video of the 8mm magnet working through a 20mm table. I imagine these magnets will be more than enough strength. Assuming they are we will go the route of testing out different washer sizes to end up with the perfect magnetism.
Super-Strong Rare-Earth RE Magnets (8mm 20-Pack)ĘC DealExtreme Reviews
Another note, I didn't initially think about it but I don't think you want any magnet in the roller blind itself. If you do, they roller blind will be all stuck together every time you pull it down.
Here are the ones I ordered
Super Strong Rare-Earth RE Magnets (10mm x 1mm / 100-Pack) - Free Shipping - DealExtreme