Yes, you can record 4K videos on Oppo K1.
No. Oppo K1 is not a waterproof mobile phone. You should be careful while using it.
Yes, Oppo K1 has Full HD+ AMOLED on-cell display.
Yes, Oppo K1 does have a 3.5 mm headphone jack and it also comes with an earphone in the box.
Yes, Oppo K1 does have the dual 4G VoLTE support. You can use 2 4G networks at the same time on this mobile.
Keeping in mind that the Oppo K1 is the only phone with an in-display fingerprint sensor in its price band, the launch price of Rs. 16,990 is not too bad.
At the price, it has great performance, a good battery, impressive cameras and much more. It is also the cheapest smartphone you can get with an in-display fingerprint sensor.