With regards to #1, you’re putting words into my mouth. I never claimed that an order came down to Charlemagne to enforce such a conversion. He did it on his own prerogative and many clergy agreed with it. The fact of the matter is that a significant number of the clergy who traveled in retinue with Charlemagne and carried out his orders to baptize the conquered Saxons. It is significant that Alcuin of York, the premiere theologian and bishop of the Carolingian Court, did not criticize Charlemagne’s actions due to the use of force. He criticized them solely on the basis that the Saxons should be further educated before their baptism. Force was not objectionable. He wrote to Charlemagne:
“Look how much in devotion and kindness you worked to weaken the stubbornness of the unfaithful people of the Saxons before the expansion of the name of Christ through the counsel of true salvation. But because the elected [the Saxons] are not yet seen to be made in that divinity, many continue to remain hither outside this [divinity] [and] with the devil are damned in sad and sinful customs.” My translation from Alcuin,
Epistulae. Ed. Ernst Dümmler, Monumenta Germaniae Historica, Epp. 4, EKA 2, pp. 157.
Charlemagne’s forced conversions as a matter of political subjugation are painted by Alcuin as good deeds. The whole Frankish clergy backed Charlemagne’s deeds against the Saxons. The only objections were only aimed at not the forced conversions, but rather that the Saxons were not educated enough in Christian knowledge and that their tithes should be lessened. If you are looking for anything regarding papal views to this, you won’t find them because during the Carolingian period, the popes largely kept out of Frankish political affairs.
Sources: Wood, Ian N. “The Northern Frontier: Christianity Face to Face with Paganism.” In
The Cambridge History of Christianity: Early Medieval Christianities, c. 600-c. 1100. vol. 3. 230-246. Edited by Thomas F. X. Noble and Julia M. H. Smith. New York: Cambridge University Press, 2008. 233-234.
As for #2, Augustine was a great and prolific writer. As such, it is difficult for me to so off-hand track down his two opposing opinions in his large body of works. I hope you can simply be satisfied with a secondary source, which talks about his change:
Brown, P. R. L. “St. Augustine’s Attitude to Religious Coercion.”
The Journal of Roman Studies 54 (1964): 107-116.
As for #3, my sources are:
Dvornik, Francis.
The Photian Schism: History and Legend. New York: Cambridge University Press, 1948. Reprinted 1970. 151-152.
Herrin, Judith.
Byzantium: The Surprising Life of a Medieval Empire. Princeton, New Jersey: Princeton University Press, 2007. 135-137.
As for #4, here are some examples of persecution of the Jews in Europe during the medieval period:
legacy.fordham.edu/halsall/source/1096jews.asp
Frankish Church Councils from the sixth to the eighth centuries legislated against Jewish commercial activities and against Jews owning Christian slaves. For this see:
Halfond, Gregory.
Archaeology of Frankish Church Councils, AD 511-768. Boston: Brill, 2010. 102-108.
In the 14th century, King Philip IV of France confiscated all the property of all the Jews in the kingdom, and then expelled them. For this see:
Madden, Thomas F.
The New Concise History of the Crusades. New York: Rowman & Littlefield Publishers, 2006. 191.
Meanwhile, in Fatimid Egypt, Jews were allowed to serve in the military. For this see:
Tyerman, Christopher.
God’s War: A New History of the Crusades. Cambridge, MA: Harvard University Press, 2006. 155.
After the fall of Jerusalem to Saladin, Saladin encouraged Jewish settlements in the city. For this see:
Runciman, Steven.
A History of the Crusades: The Kingdom of Jerusalem and the Frankish East 1100-1187. vol. 2. Cambridge, England: Cambridge University Press, 1952. Fourth Printing 1996. 381.
After the fall of Edessa, which led to the Second Crusade, Zengi helped to settle Jewish families into his new territories. The reasons for such were because the Jews felt far better treated under Muslim rule than under Christian rule. Therefore, they were loyal subjects to Zengi. Zengi installed them in order to help consolidate his new holdings. For this see Runciman also, but on page 193.
#4 is not historically controversial. I’d be happy to give you more sources, but they may very well be sources I haven’t read because it’s not an opinion I find objectionable nor in my area of focus. It’s common knowledge amongst all medievalists.
My point to all of this is simply to illustrate that people in the past, in the name of Christianity, ranging from lay people to bishops, all advocated or condoned violence in the name of advancing the Christian faith. Whether or not you think this is truly Christian or not is inconsequential. They thought it was a truly Christian thing to do.
Thoughts? 
Whenever you have more time.