I studied the Bible in seminary (Reformed--Presbyterian)...and then studied the Qur'an on my own. Honestly, there is plenty of violence in both. The one difference I found is that at least with regards to the Qur'an, the whole thing was revealed/written down in such a short period of time (compared to the Bible) and during the lifetime of Muhammad (peace be upon him). We also have a pretty good understanding of what was going on at the time the various surahs were revealed--which I don't think we have as accurate of understanding with regards to the Bible--although I could be wrong. The earliest book from the New Testament was written at least 20 years after Jesus's death with the earliest of the Gospels being written around 70 AD (usually attributed to the Gospel of Mark).
There's a really good, well-written book by Reza Aslan called "No god but Gods" which goes through the history behind the Qur'an. It talks about what was going on when different things were revealed. I think reading that will help you a lot.
In general, later in Muhammad's life, when the Medinan surahs were revelead, he was facing battles and other issues vs. the Meccan surahs when things were more peaceful (beginning of his Prophethood, flying under the radar so to speak). So yes, you can generalize like that--but it's not so cut and dry. :) With any book, it is critical to know the background and not take verses out of context. I think Americans these days tend to give the Bible the benefit of the doubt, but not so much the Qur'an.
As for contradicting itself, one example that comes to mind is the issue of drinking. At first, Mohammad (pbuh) said...don't come to the prayers drunk. But over time, the revelation became more strict and said "don't drink any alcohol". The general theory is that if he had started with don't drink, people would have thought he was crazy... they needed a more gentle approach. There might be others, but that's the one that comes to mind. OK...Googled and found this... I guess there are more.... LOL.... https://sites.google.com/site/muslimanswers/Home/contradictions