My advice would be:
First, get rid of any and all "clean my", "cccclean", "keeper", etc apps!
Carbon Copy Cloner is an app that will let you clone your system drive (or any other drives) 1:1. Keep multiple systems and boot into them when and as you please.
There may be a plugin or maybe even an interface driver that is not yet compatible with OSX 10.13. Your only choice at this point is to either go hunting for that or to do a clean install of 10.11 (which was a known working system for you).
In the long run, keeping backup clones of any system you build and not losing work (building said systems) or having downtime is the better answer. Manually installing OSX might seem like a PITA right now but it would end in success. I don't have a quick clue what might be incompatible from what you said or I'd share. It may or may not be something easy. But starting to keep your OSX installs and be able to flip back and forth between them is the thing to do. Not just having multiple systems hanging around to boot into feels like running out of gas or something.
That 2011 machine with a SSD is nicer than anything Apple sells currently and it's a faster machine than most of their newer models as well. Take care of it.
PS. Keep those installer files around! Apple tends to get severe amnesia with older software. That goes for anything useful found online for that matter. Don't ever expect to see something still there tomorrow!