hey Chris! There's a few ways of handling this. My gut feeling is that if your customers are all the same deployment with a few different configuration variables, you might want them to be different stacks:
https://www.pulumi.com/docs/intro/concepts/stack/
The information about configuration is here:
https://www.pulumi.com/docs/intro/concepts/config/
Regarding your need for build changes, that falls outside of Pulumi's scope I think, but if would be possible to build a netlify like clone with some of the cloud building blocks I think