Likely; or your logs don’t go back far enough.
No, it’s an additional task that should be done after every upgrade. Although you can add a hook to run pacdiff every time you upgrade with pacman.
Make sure you’re familiar with how diff works and vi too probably (the editor may be different on your machine) if you setup the hook above. Otherwise after every upgrade you can simply run pacdiff --find -o and it will give you a list of pacsave files you need to compare with the same file (without .pacsave) on your system and work out what changes to keep or discard depending on what you have configured.
But I suggest you get familiar with how it works first. There are a number of threads on this forum that have good discussion on the topic.
Here for example: Check and manage pacnew files
No output from --find likely means you don’t have any pacnew files to worry about (good). That output from --locate likely means you haven’t got locate configured.
Correct. But the log isn’t listing the process for some reason (it usually does). It does provide a process ID though, so next time you try it immediately after it fails. Run ps -q [PID] (replace [PID] with the PID listed in the kernel: task:Thread entry to work out which process is holding things up.