Originally your username with TT would be your full phone number at tt.net eg. 01843123456@talktalk.net and you could retrieve your password by calling a special number from your TT phone, dont know when that changed as I have been with them for a number of years. However now it is redundant as has been said.
I nd others here would be interested in how your FTTC connection goes when live, If you are having a self install then all you will have is their SuperRouter Huawei HG635. It is possible to get line stats from it but you need a special config file to load in order to be able to run DSLStats to gather data. If you are having an engineer install I guess you might end up with a BT router acting as a modem with the HG635 behind it as a router.
Anyway let us know how it goes.
Stuart