MacBook Pro crashes when plugging in 3 4k screens
When you say you know your MBP can drive 4k screens and can also drive 3 externals plus the internal, on what basis do you say this? In fact, this is well beyond what this model is officially capable of doing.

Your MBP officially supports an HDMI-compatible device, including 4K, while using one Thunderbolt Display. Or, it can  support up to two Thunderbolt displays.

In terms of actual resolution outputted to an external display, it supports up to 3840x2160 pixels at 30Hz or 4096x2160 pixels at 24Hz (HDMI), or up to 3840x2160 pixels at 30Hz on two external displays via Thunderbolt.

Of course the above is the official position. Your testing has shown you that you can exceed this, but what you’re wanting to do is beyond what I’d recommend.

You may find my answer on another question of interest, especially in terms of real life scenarios. The MBP in that question is not the same model as yours, but the overall findings still apply.