You need to think about the user experience for the first 50 people, as you are doing.

If you're not solving a problem for them, then there is no value, so the user base will not grow. It's always easy to envision a product or service which if you have e.g 1m users is valuable; but the hard part is getting there.

If your service is ONLY valuable with 1m , or 1k users, then you need to find a different reason to onboard them, so they find some different value until you get critical mass to begin delivering on your vision.

e.g Facebook started by solving the problem of who is in my year at college to flirt with (hence the Poke button, amongst other things), later it delivered alternative value. They also just "onboarded" everyone in one go, which helped. So, you need to narrow your focus to a segment of your target audience you can focus on, target, and onboard, by vertical, geography, or some other measure. Get the first 50 people, or even 5(!) people happy, because you deliver them some value, then you can start building on that start.