What’s this for? : udev.log_priority=3
The level of verbosity of certain warnings printed during the boot process - so it stays rather quiet overall.
Whats this .img file for that Manjaro standard installation produced?:
intel-ucode.img
That is the firmware (Intel specific, there is also one for AMD-Processors)
for correcting bugs in the hardware of the CPU
AFAIK
It could work without it - but it might not, or in a flawed manner.
… that is how I understood it …
research if you want to know better/more in depth
Syslinux bootloader setup, install and update is not as automated as it is for Grub.
You’ll probably have to maintain it all by yourself
(on any kernel change/update).
Manjaro (or Arch) won’t do it for you.
AFAIK