How should I set up the firewall and DHCP with an AirPort Extreme and Lion Server?

Question

I'm trying to set up a network using an AirPort Extreme as a router (connected to the WAN on one end and the LAN on the other). I understand that out of the box I will have a hardware firewall, and the ability to set up DHCP, but am unclear on what the best way to add the capabilities of Lion Server, or if there's even any advantage to doing so.

Specifically,

(1) I'd like to use Lion Server, rather than the AirPort Extreme for DHCP, mostly because the UI is much easier to use and provides finer control.

(2) I wonder if there's any reason to use Lion Server as the firewall, instead of or in addition to AirPort Extreme (or if that even makes sense).

Is there a best practice on how to set this up? Any suggestions on how to proceed would be appreciated.