First time i used let it was to inline variable declaration with assignment . Can’t remember the language.

You need to refine it yourself. Exporting raw materials are good for short term profits but you are more exposed to price fluctuations . Look at kora for instance. They seems to have a more stable economy now than when they mostly expected raw materials

Here’s the wiki article - never had an issue following that

https://wiki.debian.org/UnattendedUpgrades

Can also suggest reading the man page. For completeness and just general knowledge also read the man pages for apt, apt.conf