How do I spawn additional instances with the same configuration?
Would this workflow be completely incompatible in the case that,
somewhere in the future, one instance would start getting additional
configuration?

If having one instance with divergent configuration is a concern, it is probably worth considering setting it all up as a distribution.
While rolling your own distribution may be overkill, this provides the most &quot;future-proofing&quot; long term because you will have a base configuration in the distribution that can be overridden on a per-site basis if it becomes necessary.
Rough documentation on configuration in distributions
With a distribution, in addition to default configuration, you can even include default content.