I believe the Ramchal addresses most of your questions here:
Regarding prophecy, its words and its acts: Yet you should know that there are two characteristics regarding the prophecy of those that prophesied: The first is the content and the second is the phrasing and the words. And that is because there are surely cases in which the prophet grasps content, but he is not restricted in the words; such that the prophet can say it with the words that he wants. But there are other cases in which they grasp content that that is also restricted by words, such as the prophecies of Isaiah, Jeremiah and the other prophets that were written for [all] the generations. Those were restricted in their prophetic words to include many [simultaneous meanings]. And even in this, the metaphor varied according to the prophet's own understanding and his ways; and it even varies according to the nature of his language and his way of speaking. And frequently, prophets were given to do actions alongside their prophecies, such as Jeremiah with his belt (Jeremiah 13) and with his yoke (Jeremiah 27), Ezekiel with his brick (Ezekiel 4) and many others like those. And the content of this was that through these actions, they would arouse the higher powers that were required according to the true essence of what the prophecy - in all of its facets - was about. And then they would be prepared and stored to bring the thing out to be actualized at the time that was fit for it.
So the prophecies come from G-d, and were dictated by him. They may even have more meanings than the prophet originally understood. To quote Ramchal again:
It is possible for a prophet to miss something included in his prophecy, but it is impossible for him to imagine that which was not [part of] it: Behold it is also possible that one of the prophets will grasp something true in his prophecy, but will not grasp all of the true things included in it. For example, [regarding] the prophecy of Jonah the son of Amittai, to whom it was stated (Jonah 3:4), "and Nineveh will be overturned" - two [possibly] true understandings were included in this statement: The first was that it was the punishment destined for them according to their sin; and the second was that what would [actually] happen to them was foreseen in front of Him, may He blessed - that is that they would overturn themselves from bad to good. However if only the matter of the punishment had been truly included in the statement, once the Holy One, blessed be He, came back and regretted the [punishment], He would have revealed the thing to the prophets, and especially to Jonah - that a new decree had come out besides the first one. But since the Holy One, blessed be He, truly included both understandings in the first statement, He did not need to make a new decree for them. Rather the statement would stand according to the second understanding, and not the first. However at the beginning, Jonah only grasped the first [understanding], and not the second. And this is what they, may their memory be blessed, said (Sanhedrin 89b), "It is Jonah that did not comprehend."
What about the parts of Tanach that are not recordings of prophecies? The Talmud in Bava Basra is clear that the entire Pentateuch was dictated by G-d to Moses (though the last eight verses may have been dictated to Joshua.) The Talmud in Megillah is pretty clear that in order for a book to make it into Tanach, it must have been written with Divine Inspiration. Otherwise, even if it was written by King Solomon, the wisest of men, it is just a regular book. It also seems that we look at the entire book as being written on the same level, or else the discussion of Esther there does not make sense.
So to go through your questions:
Does "inspired" by God mean:
(1) the same as written by God?
Not necessarily, but sometimes yes. The recorded prophecies (including the entire Pentateuch) were written by G-d, but some parts of Nach were just written with "inspiration." See Ramchal ad loc for more detail.
(2) a collaboration between people and God, each providing input, both authoritative? But why would God want a collaboration when it comes to laying down His instructions?
They were either written with G-d's complete dictation, or were people prophetically relaying G-d's will. But the entire content was written with Divine assistance (and approval) throughout.
(3) that God said one thing but the scrivener wasn't always paying attention and may have written something else? Honest mistakes?
No. See Ramchal above.
(4) that scribal errors may have crept in over the centuries and we must find them and remove them?
The Rabbis put major effort into keeping the text of Tanach accurate. They created an entire masoretic system to maintain the integrity of the text as much as possible. This ensures that the words and phrases are accurate, but there definitely are cases when we are not sure about the spelling of words, etc. The main book on the topic is Minchas Shai. The Jerusalem Talmud records cases of three authoritative scrolls that each had one word differences, and the Rabbis went with the majority.
(5) that some teachings have eternal value (that's God's part) and other teachings are transitional (that's the human part), and our task is to find which is which and, at the right time, remove the second according to the political correctness of the day?
The Pentateuch is very clear that it contains the entire Torah of G-d, and nothing can be added or removed, ever. The other works of Nach were written to explain and clarify the Torah, and as such have the same validity and permanence.
