I'd consider yours to be a medium sized environment, and I'd expect ClearOS to handle it. But whether or not it will be able to do so also depends on the server hardware specs. You will have to run your own tests. Also consider joining the ClearOS forum (
http://www.clearfoundation.com/component/option,com_kunena/Itemid,232/) and community (
http://www.clearfoundation.com/Community/Home.html) in order to gain first-hand testimony by long time users.
But one thing is for sure: ClearOS is not just a replacement for your Mikrotik router OS, it is much much more. In terms of comparison to commercial OS'es it would compete with Microsoft's Small Business Server. Check out these reviews:
http://www.linux-mag.com/cache/7662/1.htmlhttp://www.itworld.com/operating-systems/87803/a-linux-answer-windows-sbs-clearos?page=0%2C0If you wisj to know how it works, please consult this overview first:
http://www.clearfoundation.com/Software/overview.htmlIn terms of security and serving, it hardly adds any new and specific techniques; what it does is take all the time-proof, high reputed and heavily used Linux applications and adds them to a unique and comprehensive pre-installed environment with centralized configuration via an easy to use web interface. Some of the security tools included are: Squid/Dansguardian, Snort, Iptables, ClamAV.
You may test ride the web interface here:
http://www.clearfoundation.com/Software/live-demo.htmlThe detailed manual may be found here:
http://www.clearcenter.com/support/documentation/clearos_enterprise_5.1/user_guide/start