Guix/GNU/Linux multi distro + GuixSD multi-site scenario

[myglc2]

These are questions about a Guix user scenario I am contemplating.

Situation:

- I have installed Guix/Debian and GuixSD on a couple home servers
  (behind a typical broadband router).

- I am running Guix from a git checkout to which I have applied personal
  patches.

- TODO I talk my friendly sysadmins at a couple organizations into
  installing Guix on /GNU/Linux distros, say ubuntu and centos.

It seems obvious that Guix supports this scenario. But it is not so
obvious what the best way to 'instantiate' it is ;)

So I have a few questions:

1) What is a practical way to get the same identical versions of my
   customized guix packages running on all the machines?

2) What is a good setup that allows me to make and coordinate changes in
   my package manifest, package recipes, and Guix version anywhere?

3) I may want to source substitutes from my home servers. Any words of
   wisdom?

You can assume that I know how to tunnel between the sites, use git,
manage remote git repos, and have a reasonable user-level knowledge of
Guix and GuixSD.

TIA - George