How do I properly setup an Extreme (802.11 n) + Express wired Network

Hello,

I have been trying to make my setup work properly for weeks now with little success. I have spoken to multiple IT professionals as well as apple care to get this working properly but to no avail. Here's my goal, I would like to have an airport network that reaches both my office upstairs and my wifes office downstairs. I would like to be able to share internet, files, and print throughout the network.

We have:
1 new Airport Extreme (802.11n)
2 new Airport Express
1 ATT micro Cell
2 Belkin 1000mbs AC power adapters
1 MacMini
1 iMac
1 Mac Book Pro
2 iPhones (1 3Gs, 1 4g)

The current and best working setup is as follows:

The cable modem in my office is connected to the Airport Extreme. I have the Belkin AC adapter connected in my office to one of the Airport Extreme's Ethernet connectors then directly to the closest wall outlet. Downstairs I have the other Belkin AC adapter connected directly to the closest wall outlet to our ATT Micro Cell. (Micro Cell must be near a window for GPS service). All the lights on the Belkin are blue which says that it is communicating at least over 100mbs.
The Belkin is connected to the Micro Cell via Ethernet and the Micro Cell works just fine. (unless ATTs server goes down and then it losses connection but thats another discussion).
I then have an Airport Express connected to the "Computer" Ethernet jack on the back of the Micro Cell. This is supposed to pass the network connection through the Micro Cell to a router. This downstairs Airport Express is setup in Bridge mode and should be working with the Extreme upstairs to provide DHCP. I have a separate WiFi network for the downstairs network. The two airports are also setup on different channels.
The other Airport Express is connected to my Slingbox and is only being used as an adapter. (it seems to work fine).

The problem:
Both networks broadcasts without a problem and I am able to connect all of my devices to either network. The problem occurs when I switch from one Airport to the other with my iPhone or with my Mac Book Pro. The device will connect to the network but when it connects back to the downstairs network it does not receive an IP address. I literally have to shutdown and restart the entire network to get it to assign another IP via DHCP.

I have been on the phone for hours with apple care and some IT professionals but with little success. The apple care people told me to "extend the network" but when I do that the Airport Express never works and the network is completely lost. I think this is because I am trying to use a wired connection and not a wireless one (I thought of using a crossover cable but havent tried that yet). I have swithced to every channel I can think of. I have tried running the express to assign a limited range of addresses but it gives me the error that I have two DHCP servers on the network and will not provide an internet connection. I have also reset everything about 20 times. I'm sure I have done other things to get this to work but I cant remember them all. Also I just recently updated everything to the latest firmware but that has only made it so I cant print over the network (bummer for another discussion).

Any suggestions? Sorry for the long description.

THANKS!