You may want to consider good old approach of trying to grow exponentially in a sustainable way. It seems that you have no pressure from VCs, you do have a use

You may want to consider good old approach of trying to grow exponentially in a sustainable way. It seems that you have no pressure from VCs, you do have a user base and a runway. You can try setting the thing up, so the costs are essentially static and do not depend on the number of users. This seem possible, since it doesn’t look like you store images or do anything heavy. You also do not need moderation, it seems.