Sales were not steady until I got over 120 items in my shop. I am always trying to add more, but since everything I make is time consuming, I find it difficult to keep the quantities up. I have had 2 customers in the last month that bought 15 items between them! That is 2-4+ weeks of work. So my aim is to try and make at least 1 item a day.
The more items you have, the more chance you will be found. So it makes sense to have as much as you can. Although, I have to say, if someone has more than 6 or 7 pages of shop, I lose interest, and am less likely to look closely at what they have. Those supply shops with huge quantities of items really overwhelm me!
I don't think there is really any magic number. I have a friend who makes gorgeous miniature babies. I urged her to open a shop on Etsy. She only put 15 items in her shop, and sold all of them! She had a niche market so it was very successful for her.
We just have to keep plugging away.