1. of course use different pools for both services
2. that is too generic, please activate logging for pppoe (winbox -> system -> logging -> +-sign -> choose pppoe -> ok) and post a log when connecting with a client to the server.
and of course be aware that you need a layer2-connection from the pppoe-server to the pppoe-client, thats why it is called PPPoverEthernet
so make up a eoip-tunnel from the server to your access-point, if they are not the same system and if they are, confirm that the pppoe-server is running on a bridge or an interface that is directly accessible from the clients, no routing between them and the pppoe-server.