Designing a high-power PCB
Consider also a distributed approach with point-of-load (POL) converters.  The idea is that you distribute power across the board at lower current and higher voltage.  Presently, you are thinking about having one AD/DC converter which outputs 5V 32A which goes directly to RPis.  You could have an AC/DC which outputs 48V 3.5A.  Each RPi has a dedicated DC-DC buck converter (the POL converter), which generates 5V 1A from 48V.  This way, you are only dealing with more manageable 3.5A and 1A currents on your board.


(Source of the diagram.)