Great pics. How cold do you want the processor to be? Oil return is less as suction pressures are lowered.

I would extend the water inlet to the bottom of the evaporator and also put the water inlet and outlet inside and outside the evaporator so the water flows through the greatest surface area of the evaporator.

I am assuming that you are working with home or camper fridge condensing units, hence the 134A. A higher pressure refrigerant would make it easier to achieve lower temperatures, but you are looking at extra cost and further design considerations.

What is the wattage of the device you wish to make cold? There was another thread in this group that I lost track of where I asked the same question.