With the final plaque warning Moses starts wit the beginning phrase he had been using "Thus says the Lord". However, he never says "let my people go" during his speech like he had before. It shows that finality of this plaque. After this one was done the people would be leaving without a doubt.
The Passover was so significant that their calendar was changed to make the month it happened the first month of the year. Just like the passover lamb is a foreshadow of Jesus, I believe having the calendar change is also a foreshadow of Jesus also since the system of years ends up as BC "Before Christ" and AD "anon domini, which means "in the year of our Lord".
Blood is a symbol of life, without it no-one can live. The blood from the blemish free lamb was a sign for the people to show they were God's children. It also was a protection for them that the plague/judgement being brought down on Egypt. Just like the blood of Jesus (who was also unblemished) protects His children that believe in Him from the wrath of God! It keeps them alive as it kept the firstborn of Israel alive.
Chapter 12 verse 12 continues to reveal to all that He is "I am Lord" the only true Lord of all could execute judgement of all of Egypt: man, beast and their gods.
The final plaque happens, all of Egypt awakes to the death that has happens and cries out. Pharaoh finally tells the Israelites to leave and take what they had been asking for. He ends it with asking to be blessed. I feel in that moment he realized that God really was the true Lord of all.
The Israelites plundered the Egyptians by asking for the silver, gold and clothing with God's favor they receive it. This fulfilled God's original promise to Abraham in Genesis 15:4 and God's promise to Moses in Exodus 3:22.
Six hundred thousand men that number not including women and children left on foot. God really blessed and multiplied His people since it started with only 70 people when the sons of Jacob and their families went to Egypt.