Yes, you can play 4K videos on Samsung Galaxy A8 Star.
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.
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 comes with a hybrid sim slot. In addition, the phone also has OTG support.
Yes, You can record slow-motion videos from Galaxy A8 Star.