The Public IP subnets your ISP provided are sufficient to do what you are trying to accomplish. Before we go further, please clarify on how you like the network behavior be as follows.
* Do you plan to setup DNS name for those servers in DMZ? If yes, then you should assign Public IP subnets to the servers instead of Private IP subnets to simplify BIND and name resolving mechanism
* Is there any DHCP or PPPoE requirement to establish connectivity to the ISP?
* Is there a ISP equipment installed in your premise to deliver this connectivity? If yes, is it modem/router combo, (pure) modem, Smartjack, Muxes, or else?
* Is there a plan to provide IPSec or SSL VPN services into internal network?
* What type of license does the 5510 have? An output from "show version" is sufficient.