You can open the folder properties dialog similar to disk properties dialog: from the main or popup menu:
It displays the folder name, full path, number of files (including those in sub-folders) and sub-folders, and the total folder size. The field In root displays information how many files and folders in this folders not including the sub-folders, and how much space they take. As for the disk, you can assign the category to the folder, as well as add any comments (they'll be visible in right ADC window when you'll select the parent folder in the directory tree.