1. It will upload ALL photos from your phone. No matter if they're downloaded or created with camera. All of them. Including videos. 2. Most of those photos and videos isn't important to be on cloud storage. 3. Google drive becoming full because of that. 4. Via Chrome browser you can't fast delete all, you need to select one by one, and I have about 4.000 items there. 5. If you use Google Photo app on phone and delete cloud pictures it will DELETE THOSE ON YOUR PHONE AS WELL. 100%, just test it