#1. Then what do you make of Proverbs 25:2?
That doesn't say that God has hidden things in his word, or put them in code, and we have to find them/work them out for ourselves; to assume otherwise is reading into the text.
God has always made his word very clear; Adam, Moses, the Israelites in the OT knew exactly what God had taught and commanded - and furthermore, what would happen if they didn't listen to, or obey, his word. How many times did folk in the Bible get into trouble/a mess/get punished because they did not believe, follow or listen to what God said? How many today get into a mess
The whole idea of "there is hidden/special knowledge that only a few can know, or work out", is Gnosticism. The NT writers were writing against this.
Do you not believe it is to the glory of God to conceal a matter?
No.
God reveals his words and his truths. It's true that sometimes we have to search, e.g for the meaning of parables, or study to understand a truth like the Trinity - but that doesn't mean that God has deliberately hidden the meanings.
And it seem that you aren't even talking about that but about some kind of clues or codes that are hidden in Scripture somewhere and we have to try to discover the and put them together to solve the puzzle.
When Jesus was transfigured, God said "this is my Son, listen to him". The OT prophets were always saying "hear the word of the Lord", and Jesus said "whoever hears my words .....", No one ever said "whoever digs for the clues in the Bible and finds them gets the prize/is more blessed than anyone else."
#2. While Jesus did do miracles and declared He was God, He did not always openly do so and or showboat His deity or power to all.
Not to the entire world, no - there was no Sky news then.
And he didn't reveal to everyone that he was the Messiah because the Jews had preconceived ideas about what their Messiah would be or do - they thought he would be a military figure who would lead them into war against the Romans. Had he stood outside the temple and said "I am the Messiah", some would have tried to seize him and make him king, or force him to declare war on the Romans. There was a suggestion that Judas betrayed Jesus because he was not the person that Judas wanted him to be.
#3. Why do you think Jesus spoke in parables?
Jesus used parables, stories about every day items or situations they were familiar with, to help illustrate what he was saying, help people to remember and identify with it and to think about it for themselves. People always remember stories and illustrations rather than lectures/factual teaching - the Jews had been repeating the stories of their ancestors for centuries.
#4. There are truths we learned that were not always so evident at a first time reading of His Word or in the early years of our life as a Christian, as well.
Yes - we see stories from new perspectives, understand more of the teaching, have new things revealed to us by the Spirit or maybe he simply applies it to our lives in new ways.
Parables have more than one meaning, and we are encouraged to study God's word, and learn more about him. There is always more to learn about our faith and about him - he is an awesome, infinite, all powerful, all knowing God; we are finite human beings with finite minds. No human baby is born knowing the alphabet, how to count; no one learning to count for the first time will then be asked to solve quadratic equations. We all learn and as we grow and our understanding increases, we learn more complex things.
This does not mean that God has deliberately hidden things, in some sort of code, in Scripture and only a few who crack the code will benefit.