I would focus on building (or buying if you have the resources available to you) a couple properties with decent traction (enough traffic/downloads that you can

I would focus on building (or buying if you have the resources available to you) a couple properties with decent traction (enough traffic/downloads that you can run timely experiments with statistically significant sample sizes). Once you're running a reasonably popular site (or app) every ad company, and their minions, will come after you and tell you why their platform is the hottest/best way for you to earn ad revs. You can learn a lot during this process (how their businesses work, who the key players are, etc). While this is happening you can also build and refine your adTech product and use the data from your site/app to prove why your new solution is the best thing going. So in other words, BE the customer for awhile, the rest will fall into place.