I'd put the AP/router in bridge mode if you're dialing the PPPoE connections from the modem, because then the router would simply act as a 1Gbps network switch, which is what you want I suppose.
You might want to change the DHCP server to the ADSL modem instead, unless this router of your's DHCP server can give the clients a custom gateway address, which should point to your ADSL modem's IP address in this case.
Usually the WAN port is meant for when you connect the router to a different subnet / Internet connection, where the WAN port will be assigned by the WAN subnet's DHCP server. In a case like this, the router will have to know that it has to route all the non-LAN traffic via the WAN port.
A setup like this is nice to have, but I won't recommend one like this if your AP is on the router's WAN subnet, in which case a bridged configuration is the better option.
Port forwarding won't be a problem in both of the configurations that I've described above. The bridged one would be more hassle free though, because you'll require a routed network between the WAN & LAN subnet if you chose not to bridge the router. If you didn't route the WAN & LAN subnets between the modem & router, then you'll have to port forward on both devices
Here is what I meant with routed:
ADSL modem is on 192.168.1.1 and is also a DHCP server that will hand out IP's between 192.168.1.100 -192.168.1.254.
The router (which is also the WiFi AP) will be assigned an IP address of 192.168.1.100 on its WAN port by the ADSL modem.
The router is not in bridge mode, and it will also have it's own LAN IP address of 10.0.0.1, and serve IP addresses with its DHCP server with a range of 10.0.0.100 - 10.0.0.254.
If you haven't specifically configured ADSL modem to route the 10.0.0.0 - 10.0.0.255 subnet via 192.168.1.100 (which is the router's IP), then the router will NAT all the connections to IP addresses other than 10.0.0.0 - 10.0.0.255, BECAUSE the ADSL modem would send the packets destined for 10.0.0.x via the PPPoE connection
So in a setup like this, I'd advise you to setup a static IP for the router's WAN port, so that you can add a static route on the ADSL modem for the router's LAN subnet.