I'm not sure that router will work for adsl lines (bt), as i think bt have to have a combined modem/router check onm the bt website they should have a list of recomended modem routers.

depending on how you have your system set up theresa few ways you can do file sharing, some routers will allow you to plug the printer directly into it so anyone on that network can log in at anytime and print off it.

or you can set one of the computers you intend to use on the network as a print server, so you'd have the printer connected to this computer and it would have to switched on if anyone one ur netwrok wants to print.

for doing file sharing accross the internet your better off looking into setting up something with remote desktop, this will let you access your computer from anywhere on the web although it has to be connected to the internet and be switched on for you to access it.