Legal Removal Request

Post: Hi I have 2 x ADC Pi and 2 x IO Pi boards stacked on a Pi 3B+. Plus there are 4 x 8-channel optoisolators to step down the 24V sensor inputs to the IO Pi's 16 x 20k series resistor inputs to step down the 0-10V analogue sensors for the ADC channels. All seem to be working well and I have tested each pin (48!) individually and a few hooked up a the same time. Now I want to package the whole assembly but am concerned about power. I intend to have a single 5V supply powering the pi, both IO Pi's and the Optoisolator boards. As I understand it the IO Pi can be externlly powered if the 5V solder link is removed Question is for the ADC Pi's. There are 5V and GND pins on each board but as far as I can see these are taken directly from the Pi. Can these be used for an external power suppply as well or would that somehow affect the 5V on the Pi GPIO. Plus, what would be a suitable power supply if each board had all pins active (ie max current draw)?