You certainly thought for a lot of things and did an impressive Job. Maybe you should publish the project on github or similar?
I did’t quite get why you copied package cache at the beginning.
Also, it never updated kernel, you did it manually. Maybe that needs fixing.
It’s on github (been there for a few years now).
I manually copied the package cache in order to avoid re-downloading all the update packages (less stress on package mirrors). I frequently test that against quite a few different VMs - I don’t want to be re-downloading all those packages each time.
Updating the kernel is one of the features I’m working on…the code for that thus far has increased the script size by about 20%. By default it will attempt to detect what kernels the user wants installed, (i.e. latest LTS, latest Stable, latest LTS plus previous LTS, etc) installing new kernels as necessary and safely removing old ones only after successfully booting into the new ones. The fact that it is a multi-boot process adds a fair amount of complexity, contributing to it taking so long. Since the script will (by default) update itself on existing systems, I never publish anything to github until it is complete and has been thoroughly vetted/tested.
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Every few years there is an option available in the LM GUI (or CLI) updater tool to update to newer major LM release when it become available.
You can follow it every time when it’s available or stay on LTS release longer and skip few interim releases. LTS will still get security updates. One note though that if you skip some major releases update later you will do few updates at the same time for example if you stayed on release 19.x, skipped 20.x and 21.x then when you like to upgrade to 22.x you most probably need to do upgrade from your update GUI tool to release 20.x then to 21.x then to 22.x (just a minor annoyance).
Still if you install LTS release and perhaps enable unattended updates you/family can use it for years without need of manual maintenance. I’m having LM on homeserver for more than 8 years now and I’m happy with it. Never had to do full reinstall from iso. I do recommend to do backup before such upgrades just in case something goes bananas (haven’t happend to me yet). Timeshift with BTRFS partitions is awesome for such task → making snapshot in no time 
For my laptop I’ve installed recently Manjaro as rolling release dist with delayed and curated updates are appealing to my taste
Good luck and let us know if you have any more questions.