New Install Question

I am about to install Untangle that should handle a total of four separate networks: LAN (no DHCP), WAN (static IP), Tech (DHCP from Untangle) and Guest (DHCP from untangle). All four will be on totally different IP subnets.

My question is this: Should I use the DMZ as the Guest network, or leave it alone and add another NIC to the box?

Thanks in advance!