Now I'm going to say something that will sound discouraging but has your best interests at heart: do you currently have 100 people who absolutely, positively could not run their business without UserApp? Or, as an intermediate goal, ten? If not, your only job is for you to go out, as an actual person rather than a web page, and recruit those users one at a time. Your service level can be stupidly unscalable -- forget "Here's our API documentation", you can literally offer "Give me your laptop and I will write the integration for you. Right now. I'm serious. You think I'm not serious? Laptop. Now." (My understanding is that Patrick Collison was doing this for Stripe in the early days.) If they stop using it, rather than doing deep analytics magic to discover what lead to their lack of engagement, you should call them up and say "Dude, I literally coded the integration for you. Level with me: why isn't this everything you need in user management? What can I implement for you to get you to revert that commit?"
After you've got 10/100/etc people who really like your service, you can start thinking about scaling acquisition channels. In the process of doing that, you'll likely optimize the living daylights out of them, and in the process develop intuitions for "This test is a priority for me to run" versus "This seems like it's likely a poor use of my time even if it succeeds."
At the moment, the cart appears to be a step or two in front of the horse.