Yes, Samsung Galaxy A8 Star comes with a hybrid sim slot. In addition, the phone also has OTG support.
Yes, Samsung Galaxy A8 Star does have the 3.5 mm headphone jack.
Yes, Samsung Galaxy A8 Star does have the support for the portrait mode.
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, You can record slow-motion videos from Galaxy A8 Star.