A full aperture 2K scan is 2048 × 1556, but it depends on the AR on the film as to what you get out the other side. If it is flat/scope/super35 etc. changes how many pixels you end up with, as does whether you are capturing sprocket holes and soundtrack in the frame which reduces the picture-area resolution.

A bayer filter does have that 50%/25%/25% split of GRB, but in practice the resolution is better than that for each channel because of the overlapping of the bayer mask over multiple photosites. It can lead to false colour sometimes though.