Read the javadocs on the method and use a bit of inspection to determine how to grab the generation builder and attach the ConfiguredFeature. Features can now have multiple placements as a warning.
Not deprecated iirc, but it's used within damageItem which already handles everything
Wouldn't matter, item damage should be handled on the container item itself just like you have done. So, where you are doing it is where it should be done if I'm not mistaken.