Where does all the chakra of Edo Tensei shinobi come from? Where does all the chakra needed for the reanimated shinobi come from? It certainly cannot come from the caster, because the scale of the chakra being used for techniques is huge. In Kabuto's case, he was controlling several Edo Tensei shinobi at once. So all the chakra they were using couldn't possibly be coming from him.

Also, when Madara broke the Edo Tensei's contract, he mentioned about "limitless chakra". Where did the chakra come from?
There is a limited amount of chakra, however, chakra replenishes so fast making it seemingly limitless. Similarly, body regeneration is also fast in Edo Tensei form.

Everyone naturally regenerates chakra. Edo Tensei people regenerate at a faster rate. We know chakra is limited, however, because the Mizukage was drained and tired after using his infinite explosion jutsu - Joki Boi