Don’t just accept a metrics goal without understanding it. I can’t emphasize this enough: the goals you and your team agree to will be hugely impactful to your work, so make sure you buy into them. Do not accept metric goals at face value. Ask why. Ponder whether or not they make sense, and what behaviors they will incentivize. Are there situations where something will feel like a good decision but the metric doesn’t move? Conversely, are there situations where you could imagine the metric going up a lot but not be convinced that the product is actually better? If so, would another metric (or set of metrics) do a better job of tracking what actually matters?
To assess for product-market fit, look at retention. Do not look at the sheer number of people using your product or feature (which can be skewed by things like how aggressively you promote it.) Retention best correlates with whether your product is valuable because it tells you whether people who tried it liked it enough to return and use it again.