Three is better than none. as long as the community exist and has some kind of activity even one post a month with three comments, you are doing your part to create a viable home for those who share your niche interest. In three months you might get up to 6 people, in 9 months 10, one year later 15. Its difficult going from passive consumer to one of the few active posters but you truly are adding value to the space just by trying.

Lemmy users like to present lemmy vs reddit usage as all or nothing, its not. Realistically you still use reddit for the niche communities that arent getting much interaction here. I do for locallama and dynavap. But ideally you cross post to the lemmy communities to add content here too so that those like you have a better chance to find a home.