The reason you get overwhelmed is because you’re looking ahead. You’re looking to the future and feeling inadequate; you know you don’t know how to handle all those problems.
And you don’t.
But you aren’t there yet. You aren’t supposed to be tackling those issues right now. Right now you are supposed to be in the present.
When my son was a baby, I agonized over what would happen once he could walk. (My niece was a 6-month crawler and 9-month walker… and that was just around the corner!)
What I didn’t realize was that, besides him being a much later walker (he was a chunky baby), there was the scooting stage, the crawling stage, the toddling-while-holding-onto-furniture stage.
By the time we actually got to the walking stage, I was ready for it. My life didn’t fall apart. My house didn’t look like vandals had broken in. It was a slow process.
Sure, some things hit you faster than you expect, but our brains jump ahead so easily that we often don’t notice we’re thinking three steps into the future.
When you feel tempted to curl into the fetal position, chuck the manuscript, or vow to never, never, never ask another probing, door-opening question of your characters again, stop. Look around you. Where are you now?
Just do what you need to do for now.
The rest will take care of itself when it comes.