What follows is more generic advice - some of it will apply to your situation, but other parts will just apply to general system situations.
The key here is to not delete stuff :0)
Also, you can ask on the forums if you're uncertain about what's safe/not safe.
If you do want to delete stuff, there are various ways to protect yourself.
Before deleting a file, rename it to something that you'll remember and move it to a place where you will see it.
The problem here is remembering what it was named, and where it came from - but you can write it on a piece of paper or make a Notepad document next to it.
Then, wait a couple of weeks. If there are not problems and you find you don't need it - then it should be OK to delete.
As for registry entries - you can backup your registry, or you can export the key that you're working on before you change it.
As for other system stuff, you can set a system restore point or you can make an image of your hard drive before making changes.
But, in the end, you have to be prepared to recover from any sort of disaster.
The easiest way is to make system images every so often - and then store them in a safe place. But this takes a lot of disk space!
Or, you can keep track of what you've installed on your system (I do it in a Notepad document), and then just backup your data. That way you can reinstall Windows and you have a list of what else you need to install. Moving the data back into the proper folders is a fairly simple task after all of that is done.
There is a Backup forum here to help discuss more complicated tasks: https://www.bleepingcomputer.com/forums/f/238/backup-imaging-and-disk-management-software/