Thank you for this question. If I've understood correctly you want to expand your infrastructure to have two different hosts: one for Phorge, and another to host repositories.

I think it's really overkill to create such infrastructure if you just have 1 git repository. Honestly the company I work for has a Phorge with 300+ repositories (some are Git, some are Svn, all are on the same server) and they still no need clustering at all, and they are happy about that. There are no performance problems and the desire was to keep it as simple as possible.

Anyway, here is the Clustering documentation if you like to try:

https://we.phorge.it/book/phorge/article/cluster/

Feel free to highlight specific problematic parts as another Question

In addition to Clustering, you can set up all Diffusion repositories in "observer" mode, where Phorge is just "watching" (cloning) the repository from whatever remote server you point it to, instead of hosting.

Phorge will check for updates from the server once in a while (few seconds to few minuets).

You will of course not be able to use Phorge to block/manage commits to the remote server, or to control access to it.

See https://we.phorge.it/book/phorge/article/diffusion_existing/