About the output file size. It depends on
- the file format JPG, DNG, TIFF,
- in case of JPG: compression rate
- sharpening mode
To get a rough file size, the app have to fix these parameters.
The pixel step movement means - for me - allow to adjust the crop handling anchor movement by one pixel. Its position actually variable only by mouse drag. It is sometimes not so fine - when I see the whole picture. The arrows operation still image jump in the Filmstrip, this is what I propose to change the dragged anchor movement by one pixel to four direction. I hope it is more clear. If you need further details, I can add some screen shot.