Windows Server 03 or 08 RRAS or A dedicated Router

I’m new to this and I’m running 3 server from my location. I have an ISP the give me 5 static IP address and i was thinking of running my dell servers on a different IP but at the same time i would like to be able to talk to all of the server in my local network. I will be running a website, FTP an a office server. I been using the building router, but i would like to know what my fellow techs think about using the the server as a router or getting a dedicated router. this is more of a concern regarding security. What will be the best way to say secure. What are the drawbacks to each solution. I will be offering FTP space for sale so keeping my customers files and other info secure will be my primary concern.