No. Oppo A3s does not have the Corning Gorilla Glass protection. Ideally, to protect the display, you should use tempered glass over it.
Yes, Oppo A3s does have the portrait mode.
No. Oppo A3s supports 2G, 3G & 4G GSM networks.
No. You can record maximum up to 1020p resolution videos with Oppo A3s.