No additional piece is needed as the Nikon NIKKOR Z MC 50mm f/2.8 Macro Lens has an accessory attachment point for the 62mm Adapter B. 

The Nikon NIKKOR Z MC 105mm f/2.8 VR S Macro Lens (Nikon Z) would be better than the Nikon NIKKOR Z MC 50mm f/2.8 Macro Lens for digitizing slides--the 105mm lens has a flatter field than the 50mm lens, it has superior optical design, and it has built-in image stabilization, which the 50mm macro lens does not have.

Unfortunately yes. Due to the crop factor in the Z30 a lot of the original slide would be cut off. It would be recommended to use a full frame camera instead or a film scanner such as this Plustek: https://bhpho.to/3RwIfIy

Yes, the Nikon NIKKOR Z MC 50mm f/2.8 Macro Lens is a great portrait and macro lens.

No. The lens will not mount as the adapter ring does not fit the following lens. Adapter Ring 52 52mm Adapter Ring 62 62mm Adapter Ring 67 67mm Adapter Ring 72 72mm Adapter Ring 77 77mm

46mm filters

Yes. It says so right in the description of the lens on the Nikon USA website: Yes, Following from the Nikon USA website: Digitize your memories. Attach the optional ES-2 Film Digitizing Adapter Set to the NIKKOR Z MC 50mm f/2.8 and turn your full-frame Z series camera into a high-resolution film digitizer. Bring 35mm film negatives or slides back to life as stunning digital images.

The Nikon HN-41 Lens Hood Lens hoods are designed to be used on the front of a lens, and they are designed to block the sun or other strong light source to prevent glare and lens flare. If light is entering the lens from the side or edge of the lens, a lens hood can reduce glare/flare, thereby increasing image contrast. (For a practical example, think of wearing a hat with a brim outside. If you are facing the sun, it may be hard to see things when the sun is aimed toward your eye line. However, using a hat with a brim to block the sun makes it easier to see and increase the contrast/clarity of the scene).