Hello!
You’re going the right way so far. The last object you need, the feather, is hidden in one of the rooms before the car scene, might be the hardest to spot.
The locked door in the factory, however, belongs to a scrapped idea, as the puzzle in it was going to be way bigger. Instead, the secret ending shows up under the electric tower during act 4 (the ending chase) if you have collected the three items. Ash tends to appear in that direction, having extra health to fight him makes it easier to pass.
Good luck with it, and see you in the other side!