Electric Paint is not a prerequisite for the Interactive Wall Kit, but it is the most popular way to create sensors. If you want to create sensors at the front of the wall, you need to use Electric Paint, have a look at how they are done. If you are creating wall sensors at the back of the wall, you can use Electric Paint, or other conductive material, like copper sheets. Have a look here for wall sensors at the back.
For an interactive wall, we'd recommend 1l of Electric Paint.