If the plane is in a BP, then I’d add a scene component at the point where you want to spawn the door. If you attach it to the plane, it will move and scale with it. No code, you just ‘hang’ the scene under the plane mesh in the component hierarchy.
As for spawning the door, you need to have the meshes in the door BP correctly positioned so that when you spawn the actor it’s pivot point is in the right place.