Definitely go for Linux! Especially in a place where number of strangers will be using it... And I'd also suggest to make only terminals accessible for users (terminal server - terminal client model) to block them from physically accessing the machine itself. Users tend to browse in non secure sites, plug various USB devices with hell knows what evil living inside... M$ is too sensitive for those evil bits and will snap eventually (you'll be lucky if one node will not spread malware to others..). In Linux you do not have to worry about any of this. Yes, there are some drawbacks considering compatibility as M$ production is not working that well on *NIX, but you can always grab a copy of WINE (if Linux alternatives are not good enough for you) or even use a virtual machine with windows preinstalled on it if you need it that much. If anyone screws with your VM you can always restore it within minutes (or as long as it takes too copy single VM file from backups..)
Linux Mint is one great choice. It's very good looking (not as good as KDE, but kde as wayy to buggy... yes, even now with the latest releases - I make it crash by doing...nothing..), very user-friendly, fast enough and has pretty much all the packages preinstalled already.
If I were you I'd have already made server-terminal model and installed any flavour of *ubuntu/mint there...
P.S. for starters you can build as separate PC (or a few) with Mint running in it/them to see how people react. Make some ads to attract customers to Linux-based hosts to try them out. If people tend to stick to them later - you're definitely good to migrate to Linux.