I do the unpopular thing, and although new players (to my table) at first gripe about it, they later tell me they love it. Brand new players to D&D don't gripe:
Each player has 10 seconds (there is a timer) to tell me what they do for the round, at the beginning of the round. I call each player out. Before I do this though, I describe what their foes are doing so they know.
With regard to the action economy, I tell players not to worry about it in that 10 seconds, but give a few tips:
1) Know you special class abilities. If you know the action economy you're capable of, you'll be ready to say the right thing
2) Don't think too hard. Feel free to ignore action economy completely and just blurt out all the things you want to be able to do. If you don't have enough actions for all of it, we'll work it out when we resolve your turn. Just make sure you prioritize what's most important by listing if first (ex: I fire off an arrow at the orc, then I move away as far as I can)
With regard to targeting: if any character specifically targets another character, and that character dies, their attack is wasted. This applies equally to NPCs and PCs, and yes ammunition and spells can be lost this way. However, if they target "the closest enemy", I use whatever enemy is closest when their attack goes off.
Also, I do not use standard initiative. I use a system of "range initiative" where folks using weapons at their ideal range go before those who are at the disadvantage. The ranges are typically: ranged weapon, long melee weapon, standard melee weapon, close quarters weapon. Most often this results in all ranged attackers going first (and at the same time), and all melee attackers going next (and at the same time). But obviously this changes when a melee attackers comes after a ranged attacker, and when spears, daggers or fists are involved.