I am at this exact stage. It turned out that building was the easiest part. I tried to promote consistently for months and I am barely at 45 signed-up users. It feels super good to get every new user, believe me. What helps me decide is a clear deadline. Mine is the end of the year, so I gave myself almost half a year to try to get users. Until then I use every promotion channel I can. From brochures to Reddit.