Remove unwanted 'system' files
I would be extremely hesitant to remove any system files on your Mac, especially since you're not even sure what many of them are. While it is possible to do what you want, I have seen many examples of people doing this and having unintended consequences.

If you're convinced that your system is taking a lot more space than necessary, then the best option to ensure you don't run into problems is to follow these steps:


Make a full Time Machine backup
Do an erase of the drive to cleanly re-install just macOS
Migrate across all the data etc you still want from your Time Machine backup