Everyting together in one go:

print map {"    $_\n"} grep {10000 > -s and -f} <c:/data/*>;

Note that I included the -f test to make sure I only get files and not directories.

1. <c:/data/*> grabs all files and directories in directory c:/data/ and returns it as a list
2. grep {10000 > -s and -f} reduces this list to a list of files less than 10,000 bytes and returns that list
3. Finally map {"    $_\n"} transforms the list returned by grep and hands it over to print

And no parentheses used at all!

As you see you can safely stack map and grep commands and as each works on the list to the right of it, you have to read this construct from right to left to get it in execution order.