Maybe a subnetcalculator can help you like http://www.subnet-calculator.com/
(you need the subnet ID in the rules).
Btw, you might want to move to pfSense before completely configuring this in m0n0. pfSense features hosts (group of hosts) and networks (group of networks) aliases. By using this you can reduce your rules to just 2 firewallrules for what you mentioned.
You can import a m0n0 config. Most items will be applied, however some items will be skipped (like traffic shaper) as they are completely different from m0n0.