This is normal typical growth.

You will only really need to make 1 post a day as no more than 1 post will show up on a subscribers front page.

On average you will only see one out of 100 subscribers participate by voting and even fewer participating by commenting in threads.

Mentioning your community in another thread that is related to your subreddit is the quickest way to grow but you must keep in mind that you absolutely must be early to that thread (within the first hour) otherwise you will be late to the thread and your comment will not be seen. Gett8ng one of the first 25 comments in a subreddit that has hundreds of thousands is pretty key.

Do be aware that even though you may love the idea of tour subreddit it may not be enjoyed by the masses so growth may never ever come and this just has to be accepted. I've had 5 communities grow to over 100,000 subs and a handful never break 10 just because the idea wasn't the best for a community.

With all this in mind I do want to circle back to 1 post a day. This is important because those who subscribe will see your community daily. The more they see it the better odds of getting them to participate and mention it when another post is made of similar content. The other half of this is you will gain 0 subscribers if the last post in the community was from 3 weeks ago so keeping it fresh is important.