No, the Nikon D3100 records video at a maximum resolution of Full HD 1080p at 24 frames per second.
No, the D3100 is not weather-sealed or waterproof. It should be protected from rain, moisture, and extreme dust during rental use.
It uses the Nikon F-mount. To use autofocus, you must use AF-S or AF-I lenses, as the body does not have an internal focus motor.
The EN-EL14 battery provides approximately 550 shots per charge based on CIPA standards.