Found this while searching for how to copy files and choose ‘No to all’ in linux (no overwrite).

 >yes n | cp -R -i /sourcedir/* /destdir

yes simply repeats a phrase (y by default) ad infinitum.
So here we just use a copy statment, forcing it to prompt before overwriting and (via yes) say no.

Thanks Glenn Arndt from Indianapolis!

(not realated, but also of interest: How to find – Size of a directory & Free disk space)
     >du – Finding the size of a directory
     >df’ – finding the disk free space / disk usage