You would need the HS-12 hood for the 50mm f1.2: https://bhpho.to/38Cleg6

The Nikon HS-9 Lens Hood (52mm Snap-On) for 50mm f/1.4 AIS is made of metal.

No, that lens hood is not compatible. Here is the proper hood. http://bhpho.to/1ibnjz3

Although I don't leave a clear filter on the front of any of my lenses, I concur with Nicholas's answer. There is a slight chance of vignetting since the hood will be further forward. Probably won't happen with just one filter. The design of this lens hood lets you reverse it and store it on the lens. Depending on which vintage Nikon lens cap you have, you can then install the lens cap on the lens hood. The filter won't prevent this. BTW, I believe the suggestion to leave a haze (or other clear) filter permanently attached to the front of your lens is nothing more than a conspiracy to get you to spend more money before you leave the store with your new lens. I've never had any problem with the front surface of any of my lenses getting damaged as a result.

The HS-9 hood works perfectly on my AF Nikkor 50mm 1:1.4 and does not suffer from the issues you mention.

It's very difficult if you use the old style lens cap. If you use the later 'pinch' style lens cap it should be ok.

It works just fine. However, not all lens caps will work with the hood in place.