As far as I know, for synthing, image orientation does not matter, but if you want the images to appear correctly in Grid View (i.e. the 2D gallery mode), make sure they are properly oriented. I do this in Windows Explorer, since some viewers will read the EXIF orientation meta data and display the images upright w/o actually adjusting the file.
As for synthing, sharp images w/ lots of texture (patterns, etc.) and at least 3MP big work best.