Since these are small devices, I think a minimal image is a necessity. What you will use is not what someone else will use.

As to caching, I tried setting one up and found out a few things.

I originally tried apt-cacher-ng:

https://www.unix-ag.uni-kl.de/~bloch/acng/

but had trouble (can't remember exactly what) and muddled through polipo instad.

I found out:

- it was a lot easier and faster than copying cached packages around

- when doing "apt-get update; apt-get upgrade" the cache really sped up multi-machine updates. The first machine was slow, the rest were fast.

- By far, the majority of cache traffic was for updates to base stuff. foo-1.2, foo-1.2.1 foo-1.2.2, etc.

- second was prerequisites for packages I needed.

- the few specialized packages I used were not updated as frequently.