First of all, Welcome to LJR.
Redhat 7.3 Bible by Christopher Negus gives a good run down on how to setup everything for the two NIC cards so you can do both. However, /10ded puts on security cap, You want to be really careful having a firewall, a webserver, and the gateway all on one computer. If a blackhat were to stumble onto your little lan, in short order you would find yourself up shit creek without the proverbial paddle.
As for firewall's, if you browse thru the security section you will find several good firewalls that peeps recommend. I personally use Monmotha's, It starts automatically whenever I connect. But the choice is yours.