No he didn't. He said "after this manner pray". He did NOT say "pray these things". Completely different. For him to have said the latter would have constradicted what he had just said about "vain repetitions".
(2) Jesus Himself prayed the same words three times in the Garden of Gethsemane.
You provide no scripture reference. Which words? Not in Matthew 16 -- the words are different. In Mark 14 it says he prays "the same words" a 2nd time, but this is probably not verbatim, but rather the same substance. If identical it would conflict with Matthew 16 which has him praying the same thing but using slightly different words. In Luke 22 it says for the 2nd prayer "he prayed more earnestly". In no case does Jesus pray "vain repetitions". He was in earnest that this cup might pass from him, but he was ready to do the Father's will.
(3) Many evangelicals use "Praise the Lord" as a substitute for "hello."
Although I've not seen this and it may well be outside my experience, I will point out that it is not a prayer. It's a greeting.
(4) What's the difference between saying a prayer or a creed more than once, and singing a Gospel song over and over again?
Now that is a good question -- contrasting a creed with a song. We are commanded to sing spiritual songs as a form of worship.
Speaking to yourselves in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord; (Ephesians 5:19)
A creed is not a psalm, hymn or spiritual song, nor group scripture recitation. The creed might be "chanted". Does that make it an 'a capella' song? I don't think so.
As I was reviewing the Apostles' Creed, I found it simplistic and did not quote scripture. I think this is the danger of confessions or creeds. Though I might appreciated what they contain, they are nevertheless characterized by what they do not contain. An excessive devotion to creedal statements may easily lead to a neglect of much important truth which is outside the range of those creeds.
And now that we have the scriptures translated into our own language (not Latin, Greek or Hebrew), we can formulate our doctrines directly and not rely on councils or church officials to do it for us in the form of creeds which establish "orthodoxy".