1. yup
2. 4 port routers are pretty normal - but 4 computers is against NTL T&C's - dunno about other ISPs.
3. Do you want to keep the phone line? (btw you don't really get a choice if you have NTL Cable TV - you still, effectively, get charged for line rental, whether or not you use the phone)
4. I'm not sure if some can do this, but I know you can't with mine
5. I stuck in the cd, followed the instructions & it worked straight away with the default settings. Getting the more advanced stuff like port forwarding sussed is a bit more complicated - but you shouldn't need that to begin with (if at all).
6. Whether you want ADSL or Cable internet, whether you want a wireless setup, whether you have a network card in the pcs you want to connect