A:AnswerI'm curious about this myself. I imagine it's going to be a while as there are pre-orders to fill first. I pre-ordered mine from BB back in August.
A:AnswerYes, the tripod mount ring is included with the lens. It is removable, but is very sturdy. No need to buy it separately. I mount it to a tripod all the time.
A:AnswerNo. The RF series of lenses only work on the mirrorless cameras. Has to do with the distance from the lens mount to the sensor which is different in mirroless cameras.
A:AnswerRF is far better and will work without a EF-RF lens mount adapter that would be required.
Even then Sigma lens may or may not work on R5 or R6 using the adapters.
A:AnswerThe Canon RF100-500mm lens is designed for the Canon EOS R series of Mirrorless cameras. The combination will get you shooting at the max frames per second for your camera with stunning photos.