Setting Up a DMZ and Internal Network with ASA 5505 and Single Switch

This is an attempt to clarify my original post which was too long.

My task is to add a DMZ to our network.

Currently, the internal network is connected to one ASA interface.

I have been able to set up a single device DMZ where one test laptop is directly connected to a spare ASA interface.

I am trying to expand the experiment to include our existing switch so I can prove that two devices can reside inside the DMZ.

My question is:

Should I be using two interfaces on the ASA and running two cables to the switch?

Or, should I somehow be using only one ASA interface and one cable to the switch?

Or, should I be using two interfaces and two separate switches (one in the DMZ and one in the internal network)?

EXTRA DETAIL ABOUT THE SETUP

The environment is:

• ASA 5505:
  • 0/0:
    • outside
    • public facing IP
    • vlan2
    • security 0
    • connected to the serviced office building main network
  • 0/1:
    • inside
    • 192.168.47.1
    • vlan1
    • security 100
    • connected to 0/0 on a ProCurve 2510G-48
• ProCurve 2510G-48:
  • DEFAULT_VLAN (came out of the box)
    • 192.168.47.50
    • 0/0:
      • uplink to the ASA 5505 0/1
    • The rest:
      • various servers
      • another switch to which our desktops are connected

My initial experiment:

• ASA 5505:

  • 0/0:
    • outside
    • public facing IP
    • vlan2
    • security 0
    • connected to the serviced office buildings main network
  • 0/1:
    • inside
    • 192.168.47.1
    • vlan1
    • security 100
    • connected to 0/0 on the ProCurve 2510G-48
  • 0/2:
    • dmz
    • 192.168.48.1
    • vlan3
    • security 50
    • connected to TestLaptop1 with IP address 192.168.48.2

• ProCurve 2510G-48:

  • As above

With NAT and access rules I got to the point where I can:

• access the internet from TestLaptop1
• access the TestLaptop1 from the internet
• access one single device in the internal network from TestLaptop1 (to simulate limited internal access)
• access TestLaptop1 from one single device in the internal network (to simulate management access)

I am now trying to add our existing switch into the mix.