Yes, Nokia 8810 4G does have the VoLTE support. You can make calls via VoLTE enabled network easily.
No. Exactly we cannot say that Nokia 8110 4G is a waterproof device. But it is IP52 certified. Means it is splash proof. You are protected up to some extent by water.
Nokia 8110 4G comes with 512MB RAM and 4GB internal storage. Hence, just like your Android phone, it has phonebook with unlimited storage.
Yes, Nokia 8110 4G does have the support for the Facebook App.