The firewall rules out of the box are fine for most domestic situations, just ensure you add the pppoe to the WAN address list and the issues relating to DNS attacks etc go away.
This is what you want. So
- set login credentials for the router
- create a vlan interface with eth1 as parent (assuming eth1 is your WAN port) with vlan id 10
- create a PPPoE client interface with that vlan interface as parent, enter your credentials etc.
- add the PPPoE interface to the WAN interface list
- check that the default firewall rules are all there
- if you have the IPv6 package enabled check IPv6 firewall rules too, they used to be empty by default, but hopefully not anymore
- plug in WAN cable