Mac the Knife,
I am with Rickity on this one. You should have the Firewall machine as your uplink on the Switch and all the rest of the computers plugged into the Switch. You do not want the network to pass though multiple computers, it kills the thoughput. (Especially for the computer at the end of the line.)
Take Care,
Richard
P.S. Start with 192.168.x.x .... then once you have the network up and running, then play with the IP Addresses.