I will be using mikrotik as a firewall, Im planning to make this setup,
modem-mikrotik(firewall)-router-switches-computer. Any other suggestions? Cause I will also block some websites and put some restrictions on our internet access. Thank you.

There's a complete Firewall section in the RouterOS Manual:
http://www.mikrotik.com/testdocs/ros/3.0/

If you want to block web pages by URL it is best to use Web Proxy -- http://wiki.mikrotik.com/wiki/How_to_Bl ... sing_Proxy