Id argue 90% of home ownership boils down to trying to keep outside air and water out of the house. If you can do both of those, you’re winning the battle.

I’d call in a separate roofer for an opinion. There are some large gaps in your sheathing where you can see the weather wrap through, and boards that have obvious signs of water damage they left in place. I would want someone else to take a look at this and confirm it’s done right.

That’s signs of a water leak. The flashing around your vent is either non-existent, or is failing.