You can remove the 'front ends' easily and these all begin with app-xxx. The app-xxx-core packages provide libraries to other apps, but not the front end - they typically go hand in hand. The DHCP service
is provided by dnsmasq as pointed out earlier... which also provides the local DNS so if you remove it it removes both
The easiest way is just to delete the DHCP range in the webconfig?? this has the effect of disabling DHCP server. Nothing else is required...as Nick points out you probably need DHCP for your WAN
If you want to get under the skin...just run 'service dnsmasq stop' and the following will prevent it from starting automatically 'chkconfig dnsmasq off'
For firewall rules, if you want to manually edit them as a last resort - have a look in /etc/clearos/firewall.conf. Then run 'service firewall restart'