Yes, the Canon EOS R features a magnesium alloy body with dust and moisture resistance equivalent to the EOS 6D Mark II DSLR.
Yes, when recording in 4K resolution, the camera applies a 1.7x crop factor to the sensor area.
Yes, by using the EF-EOS R Mount Adapter, you can use all Canon EF and EF-S lenses with full autofocus and stabilization support.
The battery is rated for approximately 370 shots per charge (CIPA standard), but can be extended using Power Saving modes or a battery grip.