Many issues with network of 2 AE and one AEBS

Question

I have a well functioning small WDS network of two airport express (AE) stations, a wireless printer, a G4 iMac and a 12" PB. One of the AE is hooked into the cable modem with an ethernet cable and is set-up as the main base station. The other functions as a remote to extend the network.
I bought an Airport Extreme N base station (AEBS). My intention is to use it as a a file server. I've attached a powered USB hub and two USB hard drives to it. I'd also like it to be available on my existing WDS network, so I needn't change networks everytime I want to access files through the AEBS.
The AEBS has version 7.0. I haven't been able to update the version in Airport Utility, because it kind of hangs up (stays at 0%) and then fails.
Problems:
1) to solve the firmware update issue: Do I need to set-up the AEBS to access the internet first? When I'm on my small WDS network, I can't see the base station, since it is setup as a separate network. When I switch to the AEBS network, obviously I do not have internet access. So how do I update the firmware? What could be the reason for the update error?
2) The AEBS file sharing network was available yesterday, but today I can not access it from my Mac (neither the Mac nor the AEBS was put to sleep or powered down during that time). I was in the process of erasing the whole HD so I could do a fresh wireless backup. The menu bar icon for the airport disc shows my AEBS disk, but I can't connect to it. I enter my password to access the AEBS network and then the connection fails. What could be the cause? Do I need to reset the AEBS everytime? Is there an automatic logoff somehwere I need to disable?
3) I tried manually setting up the AEBS to join my WDS network. I followed all the instructions: i.e. adding the MAC address of the AEBS to my main station setup and indicating the AEBS to participate in a wireless network as a remote relay and adding the main station MAC to the setup. Channels are set-up automatically. DHCP is also automatic. However, I get an eror message when updating it. Basically it will say someting to the effect that the AEBS can no longer be found. What could be the cause of this?
(Airpot Utility worked great when I added my second AE to the WDS network. But when doing exactly the same for the AEBS, I get error messages as above.)

Answer 1

I solved all my problems mentioned above. It took a while to figure out.
First I discovered that connecting the Airport Extreme N Basestation (AEBS) to an existing WDS network gave me continuous errors: I couldn't update the firmware from 7.0 to 7.1.1 etc.
So I reset my Airport Express (Ax) which was previously acting as a remote and I reset the AEBS. I kept the Ax (which was acting as a main station and is attached by ethernet to the cable modem) as is. I set up all 3 near each other.
While keeping the reset Ax and AEBS in default settings, I selected my existing Network in the airport menu icon and then I selected the AEBS in the Airport Utility and was able to update the firmware of the AEBS.
Settings for the Ax acting as a main station: WDS settings: Participate in WDS; allow wireless clients. Internet: I set connection sharing to "share public IP address". DHCP and NAT at default settings. Channel 6. ( I discovered that the main station and the two remotes need to be on the same channel!). Set up as a main station, allow wireless clients and and added Mac addresses of the Ax and AEBS. Updated.
Then I started by adding the AEBS the WDS Network created by the main station: participate in network; allow network to be extended = off. Set up as a WDS remote. Allow wireless clients. Added main station Mac address. Internet connection sharing = off. File sharing enabled. Channel 6. Updated.
Same set-up for the Ax as a remote.
Now I can access my two USB drives wirelessly over the network and each remote has an IP address.
I did a speed test over my wireless connection for internet speed. Results: Download: 9442 kBit/s
Upload: 1006 kBit/s
Answer time: 13ms
So everything is OK!