Yes, you can record 4K videos from Galaxy A8 Star's rear camera. From the front camera, you can record up to Full HD videos.
Yes, You can record slow-motion videos from Galaxy A8 Star.
Though Samsung has not confirmed about the Corning Gorilla Glass support for the Galaxy A8 Star but we suggest you to check this video to know how durable display is.
Yes, Samsung Galaxy A8 Star does have the support for the portrait mode.
Yes, Samsung Galaxy A8 Star does have the metal frame.