Ask HN: What are the KPIs a startup should focus on and what priority?

This is a very general question, but I'd like to especially focus on the key performance indicators (KPIs) for e-commerce startups. Once an e-commerce startup gains a decent amount of traction, what macro level statistics should the founder religiously focus on? I'll list the questions I want answered from these KPIs:

  Site Popularity

  Customer acquisition cost and channels

  Performance of online marketing and online social media campaigns

  Customer satisfaction

  Customer engagement level.

Also, bonus question: What KPIs do App developers/Social network sites/SaaS startups focus on?