With ~50 users, you don't need central management in my opinion. Yes, from sysadmin perspective it would be nice and professional, but on the other hand, it costs, and adds administration. Is it worth it? I'm not sure.

I really hope, that there were a good alternative for MS setup. Currently I feel that only a network file sharing, centralized directory for users (AD), and printer sharing are about the only things a little bit problematic without using MS stack. It's shame that so few file sharing / collaboration services integrate with Google authentication.