It doesn't provide the majority of my income (yet) but by far and away it provides the majority of my life's meaning. I haven't crossed the mental hurdle of sharing all my numbers publicly yet but let's just say it is turning a profit and there are thousands of happy NanaGrammers.
I got started on it at my grandfather's 94th birthday party when by brother 1-uppped my gift of live lobsters with the gift of "InstaGrandpa." He prototyped it the night before and asked me to help build it.
Working solo is a challenge for many reasons. One thing I did early was automate the customer feedback loops. I set up an automated loop to collect customer reviews (https://nanagram.co/#happy). Collecting feedback from grandparents is a bit tougher so I set up a phone line for them to dial in and leave voicemails (https://nanagram.co/#happynanas). I get a couple voicemails and reviews each week and it's like maker fuel.
Another big challenge is fighting isolation. I like to practice deep work but there's a fine line between deep work and isolation. I would've given up a year ago if it weren't for the advisor-like support from my brother and my friend Dan. I did YC Startup School last summer and that was huge as well; I remember sharing with the group that I was on the edge of throwing in the towel, then last December MRR grew by over 2X. The next big thing I plan to change in my life is adding weekly volunteering.