Yes, assuming the express (and the PLC link) is in bridge mode, you will have one network so AirPlay, AirPrint and Bonjour will work like you have one router and everyone is in range or plugged in to the ethernet.
You can use the same SSID on both wireless networks, but then you can't choose which network you are joining if you start on one and the connection is simply better.
The big downside of PLC or ethernet link is you don't get automatic switching of the base stations if a device starts on the main and doesn't leave the signal range. You can remedy this by reducing the transmit power on the main station to ensure that by the time you get to the bedroom, the existing link is lost and the device has to join the express.
Making two SSID networks allows you to know which base station you connect - not leaving it to the software to determine based on a short measurement of the two signal strengths when you "join" the network.
Whether you have one SSID or two, I would recommend selecting different channels for both transmitters as far apart as practical or consider reducing the transmit power on one if you find bad interference in between the two wireless transmitters.
Use the logs and statistics graphs in Airport Utility to see the transmit speeds and which base station your devices are connected when you choose where to place the devices and what channels to use.
The definitive steps that worked for me. I would like to spell them out as much as possible, since many forum posts will say "Set this to that" but in no way tell you how to get to a setting screen.
- Set Airport to use WPA2 security (not WPA/WPA2)
- Airport Utility > Airport > Wireless > Wireless Security > WPA2 Personal
- This may not work for everyone, especially if you have older devices
- Set Airport to do DHCP and NAT
- Airport Utility > Airport > Network > Router Mode > DHCP and NAT
- Set Airport to reserve an IP for your AiRave/Airvana
- Airport Utility > Airport > Network > "+" under "DHCP Reservations"
- Choose a high number
- Setup the Uverse Modem/Router
- Turn off the wireless network
- Settings > LAN > Wireless > Wireless Interface > Disabled
- Verify your Apple Airport is the only thing using your Uverse Modem's Router
- Settings > LAN > Status
- Devices > Clear List
- You want to only see one device.
- Set Airport in the Uverse DMZ
- Settings > LAN > IP Address Allocation
- Firewall > Disabled
- Address assignment > Public
- WAN IP Mapping > Router WAN IP Address
- Verify this worked
- Settings > Firewall > Applications, Pinholes, DMZ
- You should only see your Airport as the 'computer' in step 1.
- Since it is selected, you see the radial button pressed for DMZ
- Set up the Airvana/Airave
- Manually set the IP to reserved
- Advanced > LAN
- (May not be necessary)
- Set to use it's own MAC address
Ultimately, I resolved the Airport/Uverse DMZ issue by switching the Airport Extreme from WPA/WPA2 to strictly WPA2. Initially, I didn't have much faith in this approach, but I tried it based on ouquinn's comment. This allowed me to set the Airport in the Uverse DMZ, which I had struggled for hours to do.
Best Answer
From what I understand uverse needs their router used instead of any other. So I think you will have to put the AEBS into bridge mode and not have it working as a router. It should still serve up the hard drive as a time capsule, it just won't be doing the DHCP or DNS work for your network. The uverse router will be fulfilling that role.