I wanted to know whether it would be difficult to move CPG from webroot to a subdirectory /gallery at a later point in time, say, when I have decided to offer content other than pictures.
no problem at all, since coppermine stores in the database only the relative path of the pics within coppermine. As long as you keep the folder/file structure with coppermine the same, you can rename and move the coppermine directory at will (remember: you will have to go into coppermine config and modify "Target address for the 'See more pictures' link in e-cards" after moving/renaming).
GauGau