When Elihu states "Be assured my words are not false,one perfect in knowledge is with you" Does Elihu speak of himself?
It's very unclear who תמים דעות that you translated as "one perfect in knowledge", refers to. There many commentary opinions on this:
Textually it's difficult to say. Have your pick.
The account of Job and his friends is an interesting one, that has deeper spiritual revelation that many of us may have thought. Let's look at the key issues.
Although God describes Job as perfect and upright and one who fears Him, still, Job had some issues in his life that had to be addressed. God allows Job and his three friends to discuss his position, his affliction etc., at great length before He intervenes. We must realise that all these things happened under the Old Covenant, where God's wrath was kindled against those who opposed Him. Yet there is the element of grace afforded to the four men.
In Chapter 32 a fifth (5) man, named Elihu enters, from nowhere. Not only does Elihu mean, "he is god", but he is also the son of Barachel, whose name means, blessed of God. Elihu comes as the man of grace. In Biblical Numerology five (5) is the number of God's grace. Elihu's wrath is kindled against Job, because Job justified himself rather than God. Elihu's wrath was also kindled against Job's three friends, because they had found no answer for Job's dilemma, yet had condemned him. Clearly Elihu, as the youngest of the four, comes with an apostolic mantle. That is to say, he respects and honours the older men. He holds back his opinions and allows the older men to finish, because he knows in age, there is wisdom. Then Elihu continues to speak on the Spirit of God which is in man that surpasses man's understanding and judgement. Finally in verse 19 Elihu states that his belly is full of wine (wine is a picture of revelation) as in a NEW wineskin. Jesus said that you cannot pour NEW wine into old wineskins. Meaning that we cannot receive new revelation from God unless we first put on the new wineskin. Take on a new mind. What then follows from the mouth of Elihu, in chapters 34 thru 37, is loaded with apostolic doctrine, that is too numerous to unpack. Elihu then vanishes from the scene and God engages Job for the next four chapters. In the final chapter, Job acknowledges his shortcomings, repents, prepares an offering and prays for his three friends. In the end Job receives the double portion of a firstborn son and dies at the age of 140 ( 2x70) years.