I am new to Pulumi. I am looking at creating a new IAM user just for Pulumi. Following the Principle of Least Privilege. What are the bare minimum permissions a Pulumi IAM user would need? (I am not very well versed in AWS IAM)

it would entirely depend on what your Pulumi program is doing. Effectively Pulumi can provision any AWS resource. you can use a tool like iamlive: https://github.com/iann0036/iamlive to scope permissions for your Pulumi program