Airport Express instead of Technicolor

[#1]

Hi, I've searched for an answer on this but can't find the exact response.
I've just has fibre installed and wasn't expecting the 2 white boxes to have to be installed at my main BT socket on my kitchen work surface. The Technicolor wireless router is absolutely terrible and I now have areas all over my house with no wifi reception. I previously used an ADSL wireless router from sky on an extension BT socket in another room connected by ethernet to an apple time capsule giving me x2 wireless networks with a couple of airport expresses for music throughout the house. None of this now works!
I read that you can take out the Technicolor router and replace it with an airport express using PPPOE but just putting in your plusnet username and password but this doesn't seem to work and just keeps an amber flashing light on the Airport Express which doesn't ever connect. Does anyone have any experience of this and know if it's a setting that I haven't changed ?
If not the next steps are
1 ) Replace the Technicolor with something better
2) Buy some Powerline sockets to get the Technicolor ethernet to my Time Capsule
3) Move my time capsule into the kitchen and have a third white box on the kitchen work surface
Any ideas ?

[#2]

The Airport Express should work fine. Search on here and you will find a number of people who have it working connected directly to the BT Modem. You need to enter your username in the format "username@plusdsl.net" and your password as the one you use to login to the member centre.

[#3]

Would knowing you can put an Ethernet cable up to 100m long between the BT Modem and the Plusnet router help in any way? You could also connect them using homeplugs.