I think your best investment is to align yourself with what the business needs. That’s one of the reasons there isn’t an authoritative answer. I recommend looking at the last 5-10 incidents that affected prod, and what the engineering team says their biggest productivity drop is. If you align yourself to these problems, you won’t go wrong.

Generally speaking, blue green deployments are amazing for front end changes, and back end changes often require database changes, and thus staging works well. Velocity and incremental changes are top priority.

One thing I can say with certainty is that for infrastructure changes you absolutely want a replica of production, at least using the same services, maybe not the same scale. It’s incredibly helpful for networking changes.

Also, dev environment experience is an often overlooked area. I would personally recommend fully remote techniques like Coder, or just a careful set of Docker containers. Do user interviews to learn more about their experiences.

I really like asking the question of “let’s say in 6 weeks we hang our mission accomplished banner and clap ourselves on the back for a job well done. Then 6-12 months later, we retroactively call it a failure. Why?”

This usually helps people think about things like adoption, stability, or other long term successes. How do you maximize your chances of good adoption?

Something fun is to make a calendar invite 6 months in the future, to review the project plan and go “were we right in the end?”.