Do I need power supply totalling my current needs to maximum of my current needs?
You need to provide current to the sum of the maximum of all components.

Your powersupply must be able to handle it if all of your components try to pull their maximum current at the same time.  The only way to guarantee that is to have a powersupply that can deliver the full total of the maximum of all components.

You don't need to regulate the current to each component.  All of your stuff is designed for a regulated voltage - current will take care of itself.



Where you will have a problem is with the LM2596.

Typical LM2596 modules are designed for 3A.  Your MIG-400 motor can draw up to 10A.  The LM2596 will probably fail to deliver the required current, and the voltage will drop.

A drop in voltage will cause the Particle Photon to mis-behave - potentially making it send incorrect signals to your motors and there by causing your device to run amok.

You need a separate regulator for the motors and the Particle Photon.

Alternatively, you might either provide a second powersupply of 6V for the MIG-400 motor or switch to a 12V motor instead of the 6V MIG-400.