That's pretty much it. I want to mirror all my updates to a single server on
my LAN and have everything on my LAN apt update from it. This seems more
efficient than having everyone download their own copies.
Google told me to use apt-mirror.
....
As Andrew mentions in his reply, rsync is a good choice for this. Or something based on it. It's smarter about what doesn't need to be copied so uses less aggregate bandwidth. Lots of use-cases around the data center :-)