Archers definitely shot for accuracy and power, at relatively close range, and not in volleys. Volley fire was done in the age of gunpowder, and on TV and movies for dramatic effect. Having archers who would use different strength bows hold arrows is useless. That would just slow down and exhaust your archers. It's not like after years of practice they don't know how to shoot accurately. Combat with archers involved them firing at will, when in range, and covered by other troops, or in a defended position. They pretty much always fired straight at their target, as seen in nearly every contemporary depiction of archers.

So these archers would fire arrows at a target maybe 50ft away, as fast as they could. The targets would need to move up fairly slowly under shield cover, since it was a) terrifying and loud, and b) you needed to stay in formation or you'd get hit.

Ammo was definitely an issue. Armies would prepare tens of thousands of arrows before campaign.

From https://www.reddit.com/r/AskHistorians/comments/1e7xa3/how_expensive_were_arrows_and_how_many_did_your/

"When Henry V succeeded the throne, he immediately began restocking the royal armoury in the Tower of London for a foray into France. He set the fletchers of England to begin making arrows, and we have a record of a contract for 12,000 arrows that cost the Crown £37, 10s, which translates to about $25,000. Arrows were produced in sheaves of 24, and archers carried between 60-75 with them into battle. They were expected to be able to shoot about 12-20 arrows per minute (An archer who could shoot no more than 10 arrows per minute was considered to be unfit for military service. Each archer carried two sheaves of arrows in his quiver and the rest stuck in his belt for quick and easy access, though he may have stuck them in the ground when he was entrenched in a position (say, Agincourt.) Each archer could therefore only shoot for about 3.5-7 minutes with the arrows he had (which is NOTHING in a battle. Seriously, 5 minutes of shooting and you're outta ammo? That's crazy.), so there were wagons that were also filled with arrows, and young boys provided a constant transport of arrows from those wagons to the front lines."

That 12,000 was just one contract. He probably had many more contracts to supply his archers.

Battles in real life are nothing like on TV. Battles often lasted many hours, mostly involving small battles fought in short bursts. You'd have two lines of troops mostly marching or standing around trying to outmaneuver the other army, and a few small battles involving a few dozen men would pop up every now and then. One or two might die, one or two might get injured. Eventually one side would create a small gap, the other side might fill the gap stuff reinforcements. This goes on and on for a few hours until one side is too scared, tired, or injured to reform the line, the enemy will seize the gap, cohesion and order breaks down, and then you'd lose the battle.

In such a fight having skilled archers is very powerful. If you are standing 50ft from the enemy and getting shot at, you are stuck in that position, allowing your enemy to maneuver. It's very hard to advance under fire. If that's not enough, the archers might kill, injure, or terrify that part of the army and they may break and flee. Such a gap can be easily exploited for victory.