Acts 26:16
16 But rise and stand on your feet; for I have appeared to you for this purpose, to make you a minister and a witness both of the things which you have seen and of the things which I will yet reveal to you.
Yes, not all was revealed to him. In one of the letters to Corinth he told them the return was imminent. Yet it clearly wasn't. Not all was revealed from the start. My thought is that Israel still had a chance at restoration.
Regarding earthly Kingdoms, yes.
Jeremiah 18
7 The instant I speak concerning a nation and concerning a kingdom, to pluck up, to pull down, and to destroy it, 8 if that nation against whom I have spoken turns from its evil, I will relent of the disaster that I thought to bring upon it. 9 And the instant I speak concerning a nation and concerning a kingdom, to build and to plant it, 10 if it does evil in My sight so that it does not obey My voice, then I will relent concerning the good with which I said I would benefit it.
Often, yes. When he speaks through prophets he says do this, or else. Remember Nineveh?
Maybe, I don't know. When the fullness of the gentiles comes in, the blindness of Israel will be lifted. We can not say for certain what the fullness is. I have ideas, as many do, but that can not be proven through scripture that I see.
Depends on what it is. When the Lord Jesus Christ came, he said through the prophets what he would do, and there was no stopping him.
Was Nineveh overthrown?
Jonah 3
4 And Jonah began to enter the city on the first day’s walk. Then he cried out and said, “Yet forty days, and Nineveh shall be overthrown!”
Most people miss the point. They talk about the fish the Lord prepared. Frankly, I don't care. He is God and he can make the animals do whatever he wants, like bring them to Noah. Nineveh was not destroyed even though he said they would be.
Jonah 3
10 Then God saw their works, that they turned from their evil way; and God relented from the disaster that He had said He would bring upon them, and He did not do it.
Jeremiah 18
7 The instant I speak concerning a nation and concerning a kingdom, to pluck up, to pull down, and to destroy it, 8 if that nation against whom I have spoken turns from its evil, I will relent of the disaster that I thought to bring upon it.