Yes, you can use video calling apps like WhatsApp or Google Duo on this phone and can enjoy video calling to your near and dear ones.
Motorola Moto C has 5.0 Inch IPS display.
No. You can use only one sim card on 4G mode in this phone. You need to use 4G sim card in sim card slot one. Second slot shall use 2G sim card.
Yes, you will get a pair of headphones with this mobile phone in the box.