The majority of your questions could be answered with a "maybe" or a "possibly not" or a "that is unknown". However you have mentioned something of significance and that should be rectified now, before any VDSL2 (FTTC) service is installed --
Also I have a poor telephone line, with broadband connected, so bad in fact that answer machine messages are so bad they can't be understood.
If you are experiencing a poor quality telephony service (weak, muffled signal, hisses, pops, click, buzzes, hums), you should first check by connecting a traditional wired telephone to the test socket behind the lower front half of the NTE5/A and calling
17070, selecting menu option number 2. Listen to the line. The only thing of which you should be aware is that the line is "live". If you notice anything else,
report a voice line fault to whoever you pay for your telephone service. Make
no mention of broadband.