I would suggest reading the Agile 2 book:

Agile 2: The Next Iteration of Agile

For BDD, I suggest this five-part article series:

How Does Behavior-Driven Development (BDD) Work In an Agile Setting? (Part 1)

For a high level discussion of cross-team leadership, I suggest this article:

https://www.linkedin.com/pulse/agile-scale-requires-special-kind-leadership-cliff-berg/

For multi-team dependency management, I suggest this article:

The Agony of Dependency Management

Very best.