If the power lever is open, will this then provide fuel via the FCU AND via the EPL?
No, absolutely no.
You are limited to the engine/prop torque, RPM and temperature limits. You cannot get more power. Using the EPL does not magically bypass or increase those limits.
I suspect that, with the EPL, the best you can get is only about 70-80% power. It is there to get you to an airfield in the event of a particular kind of failure in the FCU - not to give "extra" power to get over cliffs.