Yes, each side is the collective. You and your allies are one side, your enemies are another side. You do not roll for each individual enemy.
Yes, a round of combat includes all player actions and enemy actions. Everybody gets to do their thing per round. Roll Initiative. Side A acts in full. Side B acts in full. Roll Initiative. etc. Obviously the player character gets to Act twice, so that may be AAB, ABA, BAA
You are making it too complicated. One side does 1-5, then the other side does 1-5.
The specificity of the attacks is to help you determine the attack order for the enemies, as well as to help guide your own character's actions. Avoiding archer fire while engaged in melee has a very different feel if the Melee acts first vs the Ranged, especially if you take into account the reaction penalties to avoid multiple attacks during combat.