Sophia Efthimiatou, head of writer relations at Substack, explains that it’s ok to start writing with a small audience:

You would think known writers with large audiences have it easy here, but the pressure to succeed is felt more among them. The stakes are low if you are not at all known. There is no audience to lose, only one to gain. And gain you will. Perhaps when you start your only subscribers will be your best friend, your lonely neighbor, and your aunt–who can’t even read English. And then, one day, a fourth subscriber will roll in, a total stranger. That person will be there just to read you.