Now You Can use WhatsApp in your Watch 4 and 5 series.It's still under beta have lots of bugs but if you want to try it, you can directly install it from playstore.Enter the code shown on watch into your mobile whatsapp app and you can use it.
Use Facer app for more free watch faces.Also you can create your own watch faces if you know UI design official samsung software is available for Windows.Also you can use Good Lock module for custom watch face.