How to count number of files in each directory?

Assuming you have GNU find, let it find the directories and let bash do the rest:

find . -type d -print0 | while read -d '' -r dir; do
    files=("$dir"/*)
    printf "%5d files in directory %s\n" "${#files[@]}" "$dir"
done

find . -type f | cut -d/ -f2 | sort | uniq -c

• find . -type f to find all items of the type file, in current folder and subfolders
• cut -d/ -f2 to cut out their specific folder
• sort to sort the list of foldernames
• uniq -c to return the number of times each foldername has been counted

This prints the file count per directory for the current directory level:

du -a | cut -d/ -f2 | sort | uniq -c | sort -nr