Yes, Nokia 1 have the removable battery.
Nokia 1 has IP52 certification. It is not exactly waterproof but it does have drip protection.
You can record 720p resolution videos from Nokia 1.
Yes, Nokia 1 does have the wi-fi hotspot.
The Nokia 1 is an inexpensive Android smartphone, and as you can tell from the Nokia 1 review, you very much get what you pay for.