How many wall niches can I have?
You can perfectly accent a wall with just a single niche. From there, you can have as many as the wall allows! It is a good idea to have at least 6 inches between them so that they do not get so close as to look completely out of place. The more niches you have, the more dramatic the wall will become. A great place for many wall niches is a long hallway because hallways look rather bland since most people treat it as a bridge of some sort. While in all practicality, it is just a space through which you go to get somewhere else, but you have the choice and the opportunity to make it something more.
Using wall niches is a sure-fire way to make your home look regal and unique - you deserve to have every inch look the way you want it to since it is your space to be in.