Automate Marketing Video Editing

I need an end-to-end workflow that takes raw assets and automatically turns them into polished marketing videos ready for Instagram and Facebook. The stack must revolve around n8n for orchestration and Shotstack (or a comparable cloud renderer you can wire in Make) for the edit itself.

Here is exactly what the flow should cover:
• Ingest imagery, clips, captions, and music from a cloud folder or simple form.
• Programmatically add text overlays at predefined timestamps and positions.
• Apply smooth, on-brand transitions between clips.
• Layer royalty-free background music, auto-ducked under dialogue where present.
• Export square (1:1) and vertical (4:5) versions in MP4, optimized for both Instagram and Facebook feed requirements.
• Push the final files plus thumbnails back to a specified cloud location and return the public URLs via webhook.

Acceptance criteria
1. Re-running the scenario with different source assets should consistently output fully edited videos without manual touches.
2. All logic is contained in an easily editable n8n workflow, clearly commented.
3. Shotstack render settings, audio levels, and text styles are parameterized so I can tweak them later.
4. Delivery includes a brief loom walkthrough and a markdown setup guide so my team can redeploy the flow on our own server.

Feel free to suggest minor tooling tweaks, but the core must stay within n8n and Shotstack so we can maintain it internally.