You've probably heard this one thousand times and let's make this 1001.
There's a million metrics that you can measure for Digital Marketing, but if you had to measure with limited time? Measure these three things
How many leads are you generating?
How many people know you?
The goal is to get people you are interested to raise their hand and choose to speak to you.
You can measure eyeballs, but if it doesn't translate to leads, it's pointless.
Leads are people whom you have their contact details. Dead simple.
Measure this first before anything else
How many of that leads turn to sale?
How much is that worth?
Leads, if they are bad, it won't generate sales.
That's why most Sales team accuse Marketing team wastes money. Spends so much on campaigns, but does not amount to sale.
Finally, when people buy, do they buy again?
How many are buying again?
Churn (leaving) is common norm unless it's subscription based (like Netflix etc) where they are tied to the product.
For business that focuses on Projects, win other projects as well. Introduce a new mechanism for subscription.