

I wouldn’t let that be a deterrent to starting an instance. Just make sure you understand the obligations you have as site owner when it comes to misuse. Maintain good logging and follow legal requirements (which in the US is locking down and preserving evidence and reporting to law enforcement hotlines - depending on the nature of the misuse).
No, that’s not how the new EU legislation works. The new laws build off existing Digital Services Act (DSA) and legacy E-Commerce Directive (2000/31/EC) requirements. The DSA states again that you would have to lock down access to the material (once you become aware) and then inform authorities.
All site operators maintain safe harbor with EU authorities unless those two points are broken. In both US and EU pending legislation, no requirement to scan all STLs is required, so you do not have to automatically check all files like you mentioned.