[2020] If I go to New York as soon as I enter world tier 1, what will I miss out on?

Basically what the title says. I know I cant leave New York until I finish the story there, but do I skip all the strongholds that I didnt do in the world tiers before that? Can I even go to New York before I get to world tier 5? How would it work, I just dont want to miss any story details.