How to add G-Suite domain / users to our IAM in our GCP Project?

If the users in your AD are already synced up with Gsuite then you can simply do the following

gcloud [GROUP] add-iam-policy-binding [RESOURCE]

–member [MEMBER] –role [ROLE_ID]

To set up Gsuite you will need an organization node. I don’t believe you can do that in the free tier. Hope this helps.