I run 3-5 on distinct projects often. (20x plan) I quite enjoy the context switching and always have. I have a vanilla setup too, and I don't use plugins/skills/commands, sometimes I enable a MCP server for different things and definitely list out cli tools in my claude.md files. I keep a Google doc open where I list out all the projects I'm working on and write notes as I'm jumping thought the Claude tabs, I also start drafting more complex prompts in the Google doc. I've been using turbo repo a lot so I don't have to context switch the architecture in my head. (But projects still using multiple types of DevOps set ups)

Often these days I vibe code a feedback loop for each project, a way to validate itself as OP said. This adds time to how long Claude takes to complete giving me time to switch context for another active project.

I also use light mode which might help others... jks