Putting in place PLC between time capsule and airport base station? Here is my configuration:


Living Room


MacBook Pro
NAS
Network printer
All connected to Time Capsule

Bedroom


Hifi System (with line-in)
Laptop, iPod touch (any wireless device)



As of today, the connection between the two locations is too weak (see this question) for me to use devices wirelessly in the bedroom.

What I would like to do is to add a PLC connection between the two rooms and place an airport base station in the bedroom to extend the wireless network.  

They say a picture is worth a thousand words, so check below my existing configuration and the things I want to add (green bullets and green arrows):



I then have a lot of questions...  


Will the wireless network created in the bedroom by the airport base station be an extension of the one in the living room or a new one? (first option would be easier to wander in the apartment without having to switch from one network to the other).
Will it still be possible to connect the other devices (printer, NAS) to the time capsule and would they be accessible from the bedroom (I suppose yes if wireless network is the same) and still from the living room wired network (I don't see why it would not be the case).
Do I have to connect the PCL as on the drawing or do I have to connect it between the modem and the time capsule? (edit: yes, replied to this one by myself)


I also then plan to connect the Hifi system line in to the jack connection of the airport base station.


Will it allow me to output on the hifi system songs from my iTunes library stored on MBP?
Will I be able to control it with Remote from the iPod Touch?


You can also propose other solutions which could work in my situation.
My first need was the network connection in the bedroom. The iTunes songs on the Hifi system was a bonus when I thought about Airport Base Station.
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.