There is the possibility of confusion here. I recommend your read my article (one of the authors) on Wikipedia
PPPoEoE and PPPoEoA. There are three cases to consider. The first is PPPoEoE, where PPPoE over ethernet is being used to talk to a modem over a LAN only. This may have nothing to do with communications over DSL with your ISP or more accurately, with the wholesale access provider carrier network such as BT Openreach that may provide access to your ISP’s network. If you have a Draytek Vigor modem, your router speaks PPPoEoE to the modem but your modem may speak PPPoA down the phone line; that modem can do protocol conversion from PPPoEoE to the more efficient PPPoA. With a BT accesse-carrier ISP your modem can use either PPPoEoA or PPPoEoA over DSL; it depends on your modem’s capabilities as to which is available to you, but in such a case PPPoEoA is always possible.
I have to speak PPPoEoE to talk to my modem over the LAN as that’s the only modem access protocol over LANs, and my modems don’t speak PPPoA as the Draytek Vigor does over DSL so I have to use PPPoEoA on the DSL link unfortunately (unfortunately because PPPoEoA is less efficient then PPPoA). This is an example of the third case, where a router speaks PPPoE to and maybe through a modem and PPPoE is used both on the LAN side and over the DSL link.
If you can set up fixed IP addresses for the machines on your network, then definitely do so. If someone uses DHCP, then this may simply be a router or other server handing out addresses over the LAN. Or the address assignments may have come all the way from the ISP and are communicated to the machines on the LAN by your router. In my case I have totally fixed IP address assignments and I could set the address of every machine to a certain assigned unique choice by hand but for convenience I have set my router up to hand out fixed IP addresses on the LAN. My router gets notifications from my ISP (Andrews and Arnold) by the PPP IPCP protocol (and not by DHCP over DSL) telling it what IP addresses and ranges it should be using. I ignore this information though. If I had an ISP where the ISP-assigned IP addresses changed all the time at every connection-up, then my firewall and router settings would all break and other references to fixed addresses would go wrong. If you can’t get fixed IP addresses, one IPv4 address at a minimum but more is far better, then consider changing to a better ISP.
Hope this long sermon helps.