Hello @d0zer!

My feedback will relate more to the business development and digital ad sales revenue model.

As I see it, business development will need to grow as the # of users continues to grow. Where and how will the gathered data (steps count, groups management, etc.) be stored? Will there be a need for additional employees, data servers, physical space? These are added costs to the business as it grows. Data security is also tantamount, which I'm sure will have added costs.

Projecting the costs of this build-out vs. the projected digital ad revenue will greatly assist your profitability projections. And if you're trying to attract investors, they will want to know this info (or at least have the confidence that YOU know this).

As for generating digital ad sales revenue, I believe THIS will prove your most significant challenge to the revenue model. My opinion is based on the experience of trying to generate buyers of ad space to place their banner/video ads on a website with EXCELLENT content but relatively small recognition (average 30k views p/day).
I contacted 275 companies, organizations with the goal of slicing a small portion of their ad spend to come DIRECTLY to this website.
You see, the first challenge was to motivate the ad buyers to change their placements routine away from the large algorithms (FB, Google, etc) and come direct to us. The second challenge was trying to SELL the notion that "the eyeballs will come," or in your app's case, that the users will come.
This is a very tough, two-pronged, selling challenge!

I hope my commentary has proved helpful. I wish you the greatest success. Your passion will carry you a long way...this has been my experience as an entrepreneur.

Peace and smiles