Given the amount of customer service per user, feature support, technical support and dev-ops that will be required to run this, I doubt there is any way this business could be sustainable at $29/year/user. Not to mention how you’d actually need to grow via marketing.
If I were you I would stop on this idea immediately and come up with somewhere where the average user would expect to pay $50-$1000 per month for the service. I don’t think this is a good vertical to get into. Your competition are both better than you at the bottom of the market (free alternatives) and the top of the market and there is very little left for you. And even if you do get tens or hundreds of users, it will be just as unsustainable and you’ll also have the guilt when you decide to shut it down and kick all your users off.