Performance Indicators in existing businesses that have a defined business model and market are much easier to identify performance indicators for.
Answers to the above questions are not required, but the questions are intended to give a feel for the scope of the overall question, that being: How do startups select relevant performance indicators?
Start-ups fall broadly into three types: creators, copyists and joiners.
Creators are looking to create new value for users that they can harvest as revenue. The job is all about validation (have I created value?) and iteration (if not, how can I use the learning to pivot?). They need to focus on the metrics around cost of traffic, effectiveness of conversion, depth of user engagement and retention. Why? To spot the need to pivot, and to identify the moment to scale.
Copyists take an existing model, then adapt and replicate to extend the market or/and steal market share. Their attention needs to be on brand awareness, and on qualitative and quantitative measures comparing them with the reference market maker. Why? To optimize the competitive position so that when they accelerate, the established players can't respond effectively.
Joiners take an existing supply/value chain, and create additional options. They can use large business-style KPI sets from the get-go. Why? Because they are looking to fit into a stable market and carve out a position. How do you determine the KPIs? Interview product managers in your target space.