Are you used to mac or PC ?
On a MacPro we can do 6x FullHD output (with 6 active Mini DP to HDMI adapters). With my MacBook Pro, I can connect 2 screen on the MiniDP + one on the HDMI outputs, so I can have 3 outputs with using any splitter.
On a PC with a single nVidia GPU (nVidia 1060 or higher) you have 4 outputs, so you can have 1 for MadMapper UI and 3 outputs for projectors. You can even put multiple graphics card to have more outputs. A guy did 10 outputs with 3 nVidia 1060 in the same machine...
You always have to be careful about performances. The ideal is that MadMapper is always able to do 60 FPS, so if you use 30 or 60FPS movies it looks very smooth. If using MadMapper materials they will run at 60 FPS in this case. But with a recent GPU, performances is generally not a problem on 3 full HD (with MadMapper