Initiative is no longer a thing. Dex is good enough without it. If you have a class ability that affects initiative, let me know and I'll replace it with something else.
You act in the order you have an idea to act. Enemies will go as dramatically appropriate. Surprise is still a thing that trumps. If you know what you want but can't quite articulate it, knock the table or something. That may change slightly to having you act when you figure out what the rolls and rules you need are.
Big combats are going to be abstracted. Details may vary, but the general rule is that you'll be facing the important enemies, and the supporting allies and enemies will be causing damage or other effects on an abstracted basis.