1. Not sure, but I would think you would be able to get a more comptetive deal from one of the other ADSL providers around - maybe something in
http://www.cableforum.co.uk/board/forumdisplay.php?f=63
You may also be able to get a phone/Sky/ADSL package cheaper than individually.
2. IIRC BT are usually quite good at moving numbers but you will probably have to pay for it. May be dependant on whether you new house is in a different area code.
3. If you tell NTL you want to move to PAYG dial-up you should be able to keep your ntlworld email address. Not sure if you have to actually dial-up to keep the account active.
HTH