any adsl modem with more than 1 lan port is also a router so you can use it on both rj45(by using one of the lan port) & rj11 connections.
yes.in connection settings select connection type as dynamic ip.
is your modem has interface like this?
check tp link w8968
select ISP as dynamic ip address & save & reboot.it should work.W8968 has 4 lan ports out of which one is "EWAN" port which is similar to "WAN" port in routers & this will be used for rj45 input.