The four expressions of redemption are four phases of the redemption process.
Hashem says that after the Jews are redeemed with miracles they will know that Hashem is God, isn't that obvious? Just because there are great miracles doesn't mean that people will believe, as history proves.
ויצום אל בני ישראל - what were they commanded? About the mitzvah of freeing slaves. Why were they told about that now?
Why do we need to know Moshe and Aharon's lineage right now?