1: chainmail on its own was awful at protecting from arrows. It was the combination of a gambeson and chainmail that was effective.
2: no, a vast majority of "casualties of war" were inflicted from infections, disease, starvation, infected water, and STDs. The rout was the second most lethal time of war.
3: This is true, however, you were considered an adult at 16, and most peasants would "marry" at that time as well(marriage as we do it today were only for the rich elite, the regular peasants just got a priest to declare them married).
4: true.
5: False-ish. The British longbow was used over ranges were accuracy was useless, and you earned more on making it rain, as such British longbowmen were not trained to hit targets, but areas. If you shift your attention eastwards though, such things became less common. hell, if yo look at the war of the arrows, it was pretty much a war of sharpshooters.
6: false. The longbow could be "mastered" in a few weeks, if you put your mind to it. It did however require years of training before it could be used(training, not practice), because of the fatigue from rapidly drawing the up to 150 pound draw(135 was the average, 150 was a freakishly strong one).
7: This is true, they also tended to be fatter than the rest of the army, as they carried relatively little metal equipment, and were paid more than the rest of the army, allowing them to keep a bit of a gut. Its worthy of note though that they were muscular to handle the draw repeatedly, as you don't need to be massively powerful to do so once or twice.
8: false-ish, the Saracen arrows did pierce the mail, but the mail took enough force away from the arrows to make them stick in the underworn gambeson. Oh, and aside from belts and straps, the Crusaders avoided leather like the plague, as it gets really ******* hot.
9: False-ish, nearly all knights who saw combat. Most didn't, as knight was first and foremost a social class, and not all knights ever had to go to war(likewise, many many knights died before being able to go to war, as you could be born into the role, and child mortality rates were pretty high).
10: true, you could argue the muslim invasions of Europe were for the glory of Allah, but nah, they just wanted slaves and money.
11: False, guns had several uses over bows, for one, the bang they made tended to scare horses ******** , the smoke screen they laid down masked your own numbers, and made you harder targets for all forms of counterattacks, ammunition for it was easier to transport(a small charge of powder, a ball, and some paper took less space than an arrow), bows could be completely ruined by rain, while a gun that had been oiled well enough would have no problems, and guns could fire multiple projectiles as one(grapeshot), which, while not highly effective, still gave you a better chance to hit that tricky spot right underneath the armpit on that knight you wanted dead.
12: true-ish. As guns grew more prominent, armors grew thicker and heavier. Even then, the groin, under the armpits, and at the right angles, the neck, were weak spots were a bullet could force its way in.
13: Normans advanced castle building. Castles had been built before. Otherwise yeah.
14: ... well, i guess according to the Byzantine empire, they would be the brightest military minds.
15: actually, most of them were two forces meeting up, deciding who had the highest chance to win, and the losing side going home. Soldiers didn't want to die, and neither did their commanders.
16: false, it's designed for thrusting, hence the tapered edge. It was still used after plate came around, but knights stopped carrying them. Knights instead favored daggers(that is to say, grappling+daggers).
17: false-ish, the Scottish used a sword called a claidheamh-mòr(commonly known as a claymore), this weapon was introduced during the late middle ages, and is often considered a great-sword.