There are always lots of metrics you can track. The trick is finding the right ones that provide the most value, specific to your business. In one of my past companies, we had what I thought was a killer KPI doc - many tabs, lots of metrics, and even cool trend graphs. But, we spent way too much time reporting and not using most of the info. I wish I had EOS back then.
That said, here are three that I love... that might be ones to consider for you. Certainly, follow the EOS approach first. After you've got your initial list down, I love diving in - see what best practices are in a particular industry - read blogs - etc... - really just to gut check I'm looking at the right 5 to 15 measurables. They need to be the right ones for you, not everyone else.
For consideration among your list...
Net Promoter Score (NPS)
I love this metric because it's focused on your customers. Would they refer you? You can go really granular on things like Time on Site, Bounce Rate, Social Engagement and so forth, but ultimately have you met your promises to your customers and do they like you enough to refer you to others. If you're not tracking this, this is one I recommend to almost every company. Letting customers know you truly want to hear from them and you value their feedback can in of itself be a powerful force.
Customer Acquisition Cost
As an entrepreneur, I loved dialing in this metric as it provided for a clear trigger mechanism. Of course, we had to test various marketing and sales tactics to get there. But, we knew what this number needed to be in order to scale and we tested and iterated approaches until we found our sweet spot. In one new product line launch, we started with a $200 CAC but it only took us 2 months to get it to less than $20, which was our target. It helped us realize if the product would be viable and which channels we could use to launch it.
Customer Lifetime Value
Depending on your industry and products/services, this can be a tricky metric. But, there is always a starting point. I love this metric because it puts the focus on creating a lifelong relationship versus just a transactional one, with the caveat that your intention is to build a relationship - there are some who only care about the one purchase. When we plan our marketing, we should be considering the full customer journey - from sales, onboarding, education, loyalty, referral, proactive and reactive retention, and win-back. We focus on the value of truly treating each customer well. But, it also enables us to learn which customers are most valuable and require a certain amount of budget and attention.