Thank you... yeah I was in Prague for a few days, and didn't even look for Internet access there
When you say the Jews were polytheistic, is that based on passages from the OT, or other historical Jewish works?
It is clear from archaeology, comparative history of religion and literature, and a number of "slips" in the Bible texts themselves (in spite of their monotheistic redaction), that the religious conceptions of Israel and Judah prior to the Babylonian exile were not very different from their neighbours'. Yhwh was one of El's sons (cf. Deuteronomy 32:8f, where the variation between two monotheistic corrections in the pre-masoretic and the LXX fortunately preserves an original polytheistic synthesis, as has been discussed in http://www.jehovahs-witness.com/10/66342/1.ashx for instance). To Israel he was a tutelary god just as Chemosh was to Moab (Judges 11:24). Asherah, whose worship is attested in many OT texts, was most probably his consort goddess as Anat was Baal-Hadad's. He was associated to multiple place (sanctuary) names just as Baal (cf. the expressions "Yhwh of Teman and his Asherah" and "Yhwh of Shomron/Samaria and his Asherah" in the Kuntillet 'Ajrud inscriptions). And there is evidence for a number of other gods and goddesses. For example, Jeremiah 44:17ff shows how the henotheistic reform of Josiah only put a temporary stop to the worship of the "Queen of Heavens". Interesting books to read in this regard are Mark S. Smith's The Early History of God, John Day's Yahweh and the Gods and Goddesses of Canaan, Karel Van der Toorn et al.'s Dictionary of Deities and Demons in the Bible (DDD), Margaret Barker's The Great Angel -- A Study of Israel's Second God.
I think you are correct in assessing the exclusivism of Ezra (and Deuteronomy), but it was only one opinion among many. By inserting a Moabite woman into the line of David's ancestors, the book of Ruth clearly takes an opposite stance which is also reflected in many of Genesis' patriarchal stories (e.g. Tamar, or Joseph's marriage with an Egyptian priest's daughter).
"The true God" (NWT) is definitely an overtranslation of ha-'elohim (most probably meaning "the Divine" = "God") but in most cases this expression clearly implies a monotheistic perspective.
I'm not sure what the "gem" was but I'm glad you found it...
It may surprise you, but I think you still buy too much into the OT "great narrative" which has the reader believe that monotheism was there right from the beginning and that foreign influences were necessary for the Israelites to look to "other gods". Actually the failure of Yhwh as a national god in a polytheistic perspective was what moved exilic Judaism, not to forsake him, but to raise him up to the level of the only (hence international) "God" -- ascribing him the destruction of Jerusalem by Nebuchadnezzar as a punishment, and the restoration under Cyrus as a grace. Historically monotheism emerges from the failure of polytheism, not the reverse. Messianism comes even later into the picture.