You don't need to restore a full /system or /data backup for just rolling back one app. Instead, if you don't want to wait till it's fixed automatically, simply download previous version of Google Play from here:
Google Play Store APKs - APKMirror Free and safe Android APK downloads
www.apkmirror.com
(scroll down to "All versions" and choose the appropriate package, every version should work, but use for "Android 5.0+" and if available choose "arm64-v8a" architecture. Also check if your language is listest, if not, choose a "universal" package as it should support you device language.)
and install it over the newer version. That way you don't loose your settings from Play Store APK.
The site is safe, since hash sums matches with original APK from Google.
Anyway, 28.9.13 should work now.
As for disabling Google Play auto-update: well that's a very good idea and so far i didn't investigate how to do that. The only idea that i've actually is to disable the corresponding "receiver". At least this trick worked a few years ago, but i've no idea if that would still work on modern APKs, since they are now almost all very hard encrypted.