Yes I'm sure the numbers represent pixels, easy enough to test. No way to estimate actual file size at that point in processing because file format not known, jpg or tiff, etc. The 6 bytes per pixel is a pessimistic estimate for a tiff or psd, because some degree of lossless compression will be present.
Added by edit: Oops, fooled myself with a highly compressed file, doc: status does attempt to represent file size, not pixels.
Richard Southworth