to go down to Egypt

It was common to use the phrase "go down" when speaking of traveling from Canaan to Egypt.

I will make you a great nation

The "you" is singular and refers to Jacob. Here Jacob refers to his descendants that will become a large nation. AT: "I will give you many descendants, and they will become a great nation" (See: rc://en/ta/man/translate/figs-you and rc://en/ta/man/translate/figs-metonymy)