Here are a few general and necessarily summary remarks in reply to your questions. It is hard to be very precise, as the time period and geography you are trying to cover is vast, and the answer to most of your questions could well be, “It varied”.

• What was the largest force a country could expect to be able to muster-in terms of ratio of soldiers to citizen?

A region, or a city, in defense, might be able to muster 20% of it’s population as defenders. A country could not / would not come remotely close. An offensive, or attacking Medieval army would be no-where near this. A levy or muster of the peasants, or townsfolk only happened when defending a town or village or castle.

• What sort of animals would follow an army on the march, and would they keep them long-term while encamped?

Horses, for the cavalry and pack horses, and wagon horses; oxen, to pull wagons; perhaps cattle or sheep for food supplies.

• How would travelling livestock be managed, who would tend them? Added\

Grooms, ostlers, waggoneers, drovers

• How much did soldiers rely on foraging, hunting, and acquisition-ing? Added

The attacking troops or raiders might rely on foraging and acquisitioning anywhere from somewhat to heavily. The defenders would not. No one could support any reasonable military force in Europe from hunting.

• How were supply trains managed, guarded and established?

They travelled with the army, or they had guards assigned to them and managers appointed.

• What is the longest consecutive duration one could expect an army to stay encamped in the field?

The feudal levy traditionally only owed 40 days service, but many Medieval campaigns (especially overseas ones, such as the English in France) went on for longer, which is why they did not tend to rely on the feudal levy.

• What was the typical make-up of an army? (Cavalry, footmen, pikemen, archers, knights and gentry, etc)

This varied hugely by time and place through Medieval times. For example, Richard the Lionheart’s army, which defeated Saladin at the Battle of Acre, consisted of about 54 knights, a few hundred infantry armed with spears, and 2,000 Genoese crossbowmen. The crossbows shot the horse archers to pieces. Saladin was said to have lost 700 men and 1500 horses. Crusader casualties were two men. I know of no other Medieval army with this force mix. The English tended to have a lot of longbowmen in their forces during the 100 Years War. No other Medieval army fielded longbowmen in any numbers. Early in the Middle Ages, knights fought on horseback. By the later battles of the 100 years War, English and French Knights tended to fight on foot. Later in the Middle Ages, the pike came to dominate the battlefield. Earlier it was never seen.

• Would the army handle its own construction and manual labour, would they be organized groups of military men, or civilian camp followers?

This would vary in time and geography.

• During longer encampments could one find individual soldiers planting quick-yielding crops, or tending to nearby ones?

No

• What was the typical meal for a common soldier? How did they contrast to the meals of the army's commander/s?

Again, huge variability. The common soldier would eat what civilians ate in the region, with perhaps a slightly higher bias towards preserved foods. The commanders would try to eat what the aristocrats ate in the region, but often would not manage to and would tend to eat more like the common soldiers.

• When a commander fields a large army, who does he have to help him manage it?

Sub commanders.

• Would there typically be a lot of camp followers, or a small number? Would they be forced to camp away from the troops?

All varieties existed at one time or another.

• How would one expect to receive orders while fighting in a group of men? Would there be drums, and horns? What about when there are multiple independent but allied forces?

Sometimes. Also flags. Also shouts. Also messengers.

• What could you expect a typical levy to have in his possession upon engaging in a battle? Would he be given a spear, sword, or basic armour, or would he be expected to bring whatever he could get on his own means?

Levies were not typical. They only tended to occur when defending a fortification, and enlisting the peasants or townspeople to the defense. Castles often kept “stands of arms” (often hanging on the interior walls), which could be used to arm the villagers.

• How often were soldiers neither levy, mercenary, knight, or commander, and instead a free-man being paid to fight by his own volition?

Usually. The typical Medieval Army was made up of paid professionals. This was especially true later in the period. The feudal host was too limited in duration, and indifferent in fighting quality, to make an effective army. More and more, kings encouraged their feudatories to pay instead of muster, so they could use the money to hire the warriors they really wanted.

• At what age could one expect to be conscripted as a levy, and at what age would you no longer be wanted?added

Conscripted levies were rare. If you were in a desperate enough situation that a levy was needed, all male who could fight would be expected to.

• Could one opt out of military service in most of the feudal world? At what cost? Added

At first, no, but later, yes, it became encouraged to pay instead of turn out for the knight’s service which you might owe.

• How common were accidents in camp? Such as fires, lacerations, or concussions.

No doubt as common as they are today. Disease, however, would be much more common and more lethal.

• What would a typical levy's tent be made of?

The typical levy would not have a tent. Levies were only called to fight defensively or close to home. No one called levies to go on campaign.

• How many supplies would be provided by commanders, and how much would one be expected to bring/provide for himself?

Professional soldiers, or knights who owed service were expected to provide their arms and those of any attendants, squires, or soldiers they brought with them. If peasants were levied for defensive purposes, arms would be provided (if available – if not, pitchforks would have to do.)