About STABLE

You typically track the STABLE branch via git (optionally svn for versions 11 and 12) and compiling it yourself.

You want to stick to the RELEASE version for a production machine, which it definitely sounds like you want if you're talking about 5 years. Mind also that FreeBSD 12 is expected to end support in three years, not five. Install FreeBSD 13.0-RELEASE if you want five years of the same series.
 
I am not sure is there installation option or shell script which will configure automatic updates on FreeBSD. To check and install (security) updates every day or week like Ubuntu (for example).
 
The underlying question is: Why do you want to run stable?

In spite of the naming, the high-quality production version of FreeBSD is the one called "RELEASE". It is also the one that you can upgrade easily and automatically. Even across major release boundaries. From a user or sys admin point of view, the upgrade for example from 11.X to 12.X is not really different from the upgrade of 11.X to 11.Y, both are done with freebsd-update.

Unless you want to volunteer to be a beta tester, there is usually no logical reason to run anything other than RELEASE. Here is a quote from the FAQ:

"FreeBSD-STABLE is the development branch from which major releases are made. Changes go into this branch at a slower pace and with the general assumption that they have first been tested in FreeBSD-CURRENT. However, at any given time, the sources for FreeBSD-STABLE may or may not be suitable for general use, as it may uncover bugs and corner cases that were not yet found in FreeBSD-CURRENT. Users who do not have the resources to perform testing should instead run the most recent release of FreeBSD."
 
I am not sure is there installation option or shell script which will configure automatic updates on FreeBSD. To check and install (security) updates every day or week like Ubuntu (for example).
One could leverage a cron script and the command "freebsd-update cron". Basically, this would run a cron job that does freebsd-update fetch to check for and download updates. If updates were found, an email gets sent to alert a user "you need to run freebsd-update install".

Most of the Ubuntu systems I've dealt with check but the user still needs to run the commands.

Or simply pay attention for security updates on the release channel. There used to be a -security and -security-notifications mailing lists, that you could subscribe to and get notified, but that may not yet be available under the new mailing list paradigm. But simply looking at freebsd.org security stuff is front and center.

Or directly here:
 
There are three types of FreeBSD versions: Release, Stable, and Current.

As you can see here, Stable and Current are development snapshots, which means they are for users who 1. FreeBSD devleopers 2. FreeBSD porters 3. users who wants to fix bugs or create bug reports for the next version of FreeBSD. I recommend for Release version in most cases. If you just want to try the development snapshots, why don't you use jail or bhyve on FreeBSD-Release?

Here are some resources about FreeBSD jail and bhyve:
FreeBSD Handbook-Jail
FreeBSD Wiki-bhyve

Plus, if you use Stable or Current version, you can only upgrade via building FreeBSD manually. freebsd-update can only be executed on Release.
 
If you just want to try the development snapshots, why don't you use jail or bhyve on FreeBSD-Release?
A VM will work but it's not possible to run a newer version jail. Running older versions of FreeBSD in a jail is supported. A 12.2-RELEASE jail on a 13.0-RELEASE host will work, a 13-STABLE jail on a 13.0-RELEASE host will not.
 
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