You are correct. The core is Apache-2 and only lacks very obvious enterprise features. All the important CI bits are included in the Community Edition.
There is an EE edition in the works that will have a commercial license with more enterprise features like SSO, Okta integration, etc . I don't have the exact details but the license will allow small companies to use EE for free. The next step is to release EE.
I write a lot about CI/CD at my job (unsurprising as we are a CI service). While we do have some articles about our platform itself, most of the articles you'll find are more general:
Author here. I agree that observability is really high priority.
I've never meant the numbers to represent steps or say that one point has a higher priority than others (maybe I didn't make that clear enough in the article). In theory, you would be following all/most of the points while you prepare the monolith for migration.