I have a knowledge of CALS but
Every time I've given an answer, folk will dredge up the other answer at Microsoft. If Microsoft can't have one answer, why would you expect me to get you the answer?
My experience in this area is simple. We get more Windows Servers online. Linux is nice and free but the lost time fiddling with it means we lost sight of our goals.
BUT if you want to run a FTP site, and you can run it without integrating the user accounts with a Windows server then that is something we can do in about 30 minutes.