I have 2 (CC and Codex) running within most coding sessions, however can have up to 5 if I'm trying to test out new models or tools.
For complex features and architecture shifts I like to send proposals back between agents to see if their research and opinion shifts anything.
Claude has a better realtime feel when I am in implementation mode and Codex is where I send long running research tasks or feature updates I want to review when I get up in the morning.
I'd like to test out the git worktrees method but will probably pick something outside of core product to test it (like building a set of examples)