Maybe we should go back to the problem you are having with the Update Readiness Tool.
It appears, after you downloaded the file and double click it, you get a message about what program to use. This is abnormal just by itself. If you could get it to run, it might fix your other problems.
So, on the desktop, hold the shift key and right click. Select "Open command window here" from the context menu (this will
not be an administrative window).
Type
wusa /? and hit enter. A separate window should open with the switch optons for the command.
If another window does not open or you get some type of message, then do a search of your system for
wusa.exe and there should be 8 entries with 4 having an additional .mui extension (x64 system).
If you don't have one in the
Windows\system32 and possibly the
Windows\sysWOW64 folders, we need to get those back.
This is a
Microsoft website that describes how the installer works, but don't worry about expanding any updates to a temp folder as it mentions.