1. If your board doesn't have a special requirement about isolation (medical device etc.), your USB connector shield will touch the chassis. The chassis should be connected to PE at some point for human protection. And you will connect USB connector shield pins on your board to DC ground return plane. So all of them will be a short on the schematics. But the exact shorting points in the layout need some experience.
2. Yes. USB, ethernet and other connectors as well. You need to connect ESD protectors close to the connectors, and their ground pins close to the shield. So that the ESD transient path will be very short to the chassis.
3. Generally you can connect them. Be careful about the isolation requirements if any. If you have a desktop computer, you can check the ground and PE connections with a multimeter (when the PC is not energized) and apply the same rules if you are not sure what to do. Computer hardware usually complies with many international standards.