A simple idea that makes sense. Good luck! I see a use case and would install if there was an android version. How does adding others work? Scan QR code? Search their pre-added contact info?

For pricing, and I understand you may be bootstrapped and seeking to be cash-positive, 100 contacts limit seems really low, especially given a selling point on your website that this can be for quickly adding new contacts/business cards/high number of low familiarity/frequency contacts. Perhaps make fees for power user features, like groups, or very high contact lists, or corporate use cases?

For vanity url usernames, I'm not sure if this works or just fragments namespaces more. I have my own firstlast name .com, Twitter and handful of other social media vanity url accounts. But names are not unique being first mover is. My vote on the jury for this feature is out.