In general, stacks are identical apart from config... the only different is the Pulumi.<stack>.yaml file...

I've created a bunch of Azure infra, and so far I've been managing everything within that project/stack. I'm using multiple k8s clusters now and Pulumi's handling of CRDs is completely screwing things up trying to install identical things (like our API gateway helm chart) into multiple clusters, so I was going to start breaking the clusters out into their own stacks within this project

should that really be separate projects?

As tenwit said, the only thing different for these instances is the configuration. It is possible to add conditional infrastructure into your plan based on the

pulumi.getStack()

value, but this could be an anti-pattern.

So re-reading your last message, yes, it sounds like you want multiple projects. You can centralize some of the resources in a

shared-infrastructure

or

shared-project

project and export your outputs for the other projects to use via StackReferences.