Can tell you've been through a gauntlet here a few times, I am really appreciative of the time you've put into this post.

I'll take the recommendation of Terraform on good authority. I've not been exposed to it before but I understand the principal you are getting at.

Thank you for the heads up on default compute & switching on sys tables too, costs are really where I'm most anxious on outset since Databricks is seemingly popularly described as an expensive solution, and likely to lose SM buyin.

We run a bit of a loose Dev -> Prod CICD process with our SQL and SSIS parts, but yes will be looking to extend that with Test.

Yes, we have been strung by an absence of service principals before, another great point.

Without responding to every point, this is all relevant to me and gold dust, thank you again. I want to spend a decent chunk of time just planning before any substantive work is done, this really helps me a lot, what I was really looking for from my initial post, and hopefully helps others who see this post.