Do you have any USB3 devices which you need to run at full speed? It's not like they won't work using USB2- just slower.
Maybe disable USB3 in the bios to get the scanner working, gain some confidence using Debian, and upgrade later.
That way you will allow time for any bugs in Stretch to get knocked out.
I upgraded one machine and installed on two others, but that's not to say you are guaranteed to have no problems.
I have to refer you to the small print:
https://www.debian.org/releases/stable/ ... ading.html
One question would be: did your friend install any third party software or repositories?
Backup your data to disc or USB drive before attempting an upgrade or fresh install.
I would try an upgrade first, but have installation media and drivers to hand so I could do a fresh install if necessary.
You either need to have another computer available to download required files and ask questions if you have problems, or a LiveCD/LiveUSB available which you can use to boot and access the internet.
You also need to know how to enable repositories for any non-free software required, and possibly how to manually install a package if you don't have an Ethernet connection and you need a non-free wireless driver.