Best Practices for Structuring a Second Brain Using Obsidian or Walrus Across LLM Models

So who here has seriously built a second brain that they use for their clients, their own personal development work and maybe a work. Are you all using Claude Code and Obsidian for that? Or are you using something like Walrus so that it can retain memories across different LLLM models? What are some best practices on structure? How would you structure it so that it becomes clear and usable? I'm looking for some ideas on how to do this. Do you have a different vault for work SOPs that can be used across projects, for individual clients, for any personal development goals?