I was curious, in the Middle Ages in terms of warfare,armies and more. I have a lot of questions, so hope a few people can help!

First off, starting a war. Would Army A send a message saying "We're fighting"to Army B, or simply charge into their lands in a blitz attack to catch their enemy off guard? What were some reasons for war, aside from gold, succession or land(or were those the only ones)?

What percentage of the population would be culled for the armies? Were older veterans ever called in for their experience? Or did they only ever expect and choose young men to fight? Were numbers the main thing that the lords wanted(even if the men were old or young, as numbers were the most important thing for victory)or was training and armour just as important?

Were the population given helmets or even light armour?(Full plate being heavy, things like chainmail or something being lighter)? How about weapons, like footmen provided with spears and swords? Or were they expected to grab up or make their own? What kind of training were they provided with? Were they taught battle maneuvers if they were just commoners, like a shield wall or anything? Or was Army B just telling them "Heres a stick. Stab that fully armoured knight!" Were the commoners expected to come in and train for a few days with someone from their lords castle, or were they trained in the years before, were they just tossed into combat unprepared except for knowing hack and slash?

How many common people would be involved depending on the lands? How many knights? Did the common people or knights ever say "I don't like this cause for your war with the other kingdom Lord A" or "King B, this is a bad reason to fight!" Or "You're evil!" or "I don't want to go!" Would this be treason?

Did the invading army of A ever engage in looting, plundering, murder or rape of commoners from B or vice versa? Was there a reason for it, or was it just cruelty because they had the lord or kings backing and "to the victors go the spoils"? Did the ruling person just turn a blind eye to it because these were their fighters? Or did they punish those who abused their power?

Were battles just about crashing against each other until one side was all(or mostly)dead? Or was it a big tangle of fighting people? Did archers ever shoot into the mass of people(example: "We have reserves"from "Braveheart".) Or did cavalry fight first, then footmen and archers joined in, etc;? How did a leader make commands to all his different men across his army?

Would soldiers ever attempt to capture commanders, knights or people in a position of power from the other side of the battle? Or was it easier to kill them to make Army B lose heart and run away? If common people/footmen surrendered, would the other side take them prisoner? Or execute them because they couldn't handle feeding them?

If one of Army A's lords died and his troops ran away from the battle, would they be considered outlaws or traitors and executed? Or would they join up with another of Army A's lords and fight on his side?

Were mercenaries ever used to fight in armies? Or were they considered untrustworthy or ill trained?

Bonus question!: Were knights only ever made by a king? Who were people who could knight them? Would people ever be knighted even if they hadn't completed being a squire or been a knight in the first place(like for saving their lord, etc;)Was it only lords or a king who could raise them to power?

Thanks in advance!