Hello
For me I follow one single metric which is revenue, I don't knew if that is correct or not.
What's your most important metric?
We help authors maximize the number of Amazon reviews in the 72 hr period after they launch their book. So the median # of Amazon reviews we generate for an author in that 72 hr period is our most important metric.
If authors are not happy with that number, they are not coming back to us. Revenue and everything else follows pretty nicely as long as that metric is solid.
Monthly Recurring Revenue (MRR). The easiest one to know if a side project is worth your time on several months/years.