Hi Gem,
Keep shining in processes and communication 
- that is often the glue that ties everything together.
Perhaps you can find inspiration in the model I outlined wrt. topics of coding, business know-how and exploration here: Explore, Code and Business | Complexity is a Matter of Perspective or perhaps the agile quadrants could apply here too. Especially if you already use it 
For span-of control for senior and principal staff Iām currently exploring based on Pioneers, Settlers, Town Planners [Wardley] | by Itamar Goldminz | Org Hacking | Medium , the Team Topologies book https://teamtopologies.com/ and the Staff engineer book https://staffeng.com/.
there might be something in these threads too: QA levels and responsibilities of each and What is a Principal Tester? with Jitesh Gosai
cheers, Jesper