If all the livestock died during Plague #5, what animals had boils in Plague #6? It seems as if there is a difference made between livestock and animals. Perhaps the animals with the boils were household animals or other animals not considered livestock.

After the plague of boils, Pharaoh doesn't harden his heart, it is God who hardens Pharaoh's heart.

During the plague of hail, again livestock is mentioned. Some time must have passed since Plague #5 for them to have livestock. They could have acquired more animals from outside the city of Egypt and from the land of Egypt. (Egypt is the city. The land of Egypt is the surrounding fields and country.)

In Exodus 8:25, Pharaoh tells Moses they can sacrifice to God but to do it within the land. Moses responds with saying that sacrificing animals in the land would be an abomination to the Egyptians. What he means is that the very animals that the Hebrew people would be sacrificing are the animals that the Egyptians considered "gods".

In the plague of darkness, it says that the darkness can be felt. What kind of darkness can be felt? Praise God, that Jesus is our Light!

1 Pet 2:9
But you are a chosen people, a royal priesthood, a holy nation, a people belonging to God, that you may declare the praises of him who called you out of darkness into his wonderful light.