Theodosius: Ironically, it was the religious influence of what would later be known as the Greek Orthodox Church (which Theodosius was a member of) who converted the Germanic tribes to convert to Arian Christianity in the first place.
Elijah: When you look at II Chr. 21:12-15 and II Kgs. 2:1-12, you will notice the two texts are written by two different authors (primarily given away by the way each text tells the story). Many scholars think II Kings is much older than II Chronicles, so the writer of Chronicles could have gotten things wrong; or he could have known of a story about Elijah and Jehoram that the author of Kings didn't know about; or the story about Elijah in II Kings was made up. Whatever the point, we don't really know which is true (though most Jews and Christians have thought the II Chr. Story happened first and the II Kgs story is the end of Elijah's ministry/existence on earth). When you look at the stories side-by-side, there are many major differences in each story, most notably the chronology. II Kings has Ahaziah being king of Judah, then his brother Jehoram; but II Chronicles has Jehoram becoming king of Judah, then killing his brothers, one of which is Ahaziah. Now, who was king first? Was Ahaziah actually a king, ever? So your story about Elijah is as good as anyone elses'.
About what Jesus said about no one ever going up to see God, like a lot of what the Old and New Testaments say, we don't exactly know what Jesus is getting at. I mean, we get His point (He is the only one who can truly reveal what God is like because He's the only one who has seen Him), but Jesus could have been exaggerating for the sake of emphasis (Moses saw God's back WHILE being alive on earth, and seeing God's back still counts as seeing God). Basically, when it comes to the "facts" of who's seen God, we don't really know what Jesus was talking about.
Jesus: There's a difference between Jesus praying to God on a regular basis and Jesus praying to God before He did miracles in order to do them. We find Jesus praying to God before doing a miracle only once--the raising of Lazarus that you pointed out. But He didn't ask for power; like I said previously, Jesus thanked God for always listening to Him and He pointed out in His prayer He was only praying right then for the sake of those listening to the prayer, not for His own sake. As for Jesus praying to God all the time, it's really no different than Caesar (who claimed to be god on earth) praying to the god Jupiter, or, when there was a king, the king of Israel praying to God, even though one of his titles was "son of God" (this at first doesn't seem like people saw the king as divine, and they didn't, but they viewed the king as being on intimate grounds with God all the time because of his position, as if the king of Israel and God played poker every night and sat up watching T.V. kind of thing).
The issue that puzzles you: Why do you think so? This is something of a fallacy. It is basically implied then that humanity is not allowed to mature, progress, or broaden their thinking; they either need to know everything now (or be able to grasp it all at once) or not know anything at all. (I realize you did not say that, nor do you probably think that, but that is the logical progression of your argument.)
So let me ask you a question? Lets suppose for the moment that you believe in the Trinity (I don't know if you do): do you think you have a handle on It? Do you think you totally and completely understand the idea of the Trinity in all its multifacted concepts and components? Because I don't, and most Christians are still wrestling with this theological idea even to this day. I think God reveals things at the pace humans in general can take them (and I think their environment has something to do with it, too); otherwise, we wouldn't accept them because they didn't make sense to us and looked kind of stupid. So maybe the Trinity idea is what could be called "progressive revelation"--still real for all time, but only recently revealed because it was the right time to introduce it or (doubtful) we were ready for it:)
Hope this helped ya':D