Yes they stack. I had one fridge power unit powering 3 "tops". one ontop of the other and one to the side. Seems as long as you can make sure they are connected you can stack how ever name you need around the power unit.
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^ is what i had.
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From the wiki:
If a survivor is not hurt, or very close to full health, they will look for low tier food (cornBread, eggboiled, 1 unit each time)
If they are slightly hurt, they will look for medium tier food (cornBread, grilledMeat, boiledMeat, 2 units each time)
If they are badly hurt, they will look for high tier food (meatStew, vegetableStew, 5 units each time)