Dear Dan,
Thank you for your update.
Oh dear, sorry about the crash and lost while editing.
Long live notepad, copy and paste, and all that super-simple-local-text-jazz. I avoid editing in non-local storage.
Nope, not Design Automation at all, much simpler; to just access the model files, the Data Management API ought to suffice:
https://developer.autodesk.com/en/docs/data/v2/overview/
The Data Management API provides a unified and consistent way to access data across BIM 360 Team, Fusion Team (formerly known as A360 Team), BIM 360 Docs, A360 Personal, and the Object Storage Service.
With this API, you can accomplish a number of workflows, including accessing a Fusion model in Fusion Team and getting an ordered structure of items, IDs, and properties for generating a bill of materials in a 3rd-party process. Or, you might want to superimpose a Fusion model and a building model to use in the Viewer.
I believe the Forge translation process and the Design Automation API are the main points of cost in the process, so I can imagine that the Data Management API might possibly save you expense.
I hope this helps.
Best regards,
Jeremy