How do you measure your unit economics?

There's so much complexity in measuring LTV / CAC usually. Firstly, what really goes into CAC? Do you include salaries? If so, how do you measure channel-based CAC, and attribute salaries to that? Secondly, if you haven't been around for long enough, how do you understand your churn rate for LTV calculations? Use benchmarks, or rough estimates? Finally, we've all come across the holy benchmark of unit economics: "3:1 is the perfect ratio". But that was from when Paul Graham (?) mentioned it in a blog a long time ago. Does it still hold? Should there be different benchmarks based on the industry, business model, etc? Just wanted to start a discussion to see what everyone things.