Interesting question, even if unfairly weighted. If you do not accept that Jesus is God, then the idea of His being the Messiah makes no sense, if you do, it fits perfectly.
The reason I believe Him to be both, is because of the resurrection. Paul says in one of his letters that if it is not true, then Christians should be pitied. If it is true, then Christianity is true, and it only remains to work out the details; if false, then it is a complete waste of time.
This clearly follows, because the resurrection proves Him right in what He said. He accepted worship, claimed the authority to forgive sins, and ultimate authority as a lawgiver. He also claimed the title 'Son of Man', a reference from Daniel believed to refer to the Messiah, and claimed to be greater than David.
This is something our modern culture doesn't understand, as we see no difficulty in someone surpassing their predecessors, but in His time, the opposite was considered to be true. So, when David said "the LORD said to my Lord", he was implying that the Messiah (his descendant) is greater than him; yet, how could this be true, unless the Messiah came before David-which him being God would achieve.
Also, you used the fact that you do not believe him to be God to claim some 'unfulfilled' prophecies-for instance, that knowledge of God would go throughout the world. Clearly, if He is God, this is happening.
Also, you say that He was not descende from David, yet the New Testament makes it clear that He was-that was why 2 of the gospel writers felt it important to provide a genealogy. This also leads to an interesting question, if the Messiah hasn't come yet. As the records of ancestry were destroyed when the Romans sacked the Temple in A.D.70, how would God prove this prophecy to be fulfilled in the Messiah? And if you are saying that it doesn't matter, because by now, surely all Jewish lines have intermingled, then why would God give this prophecy. Surely the most reasonable line of thought would be that the Messiah came while there were still records that could be referred to.