Here is something that is interesting... when the Agothacles invades Africa (or whatever the title is) comes up... is that movement to Africa if played as an event considered Naval Combat?
No, that is why the event text says "Place Agathocles..." instead of "Move Agathocles..."
Also, the only way that the Greeks can get a foothold into Africa is with this card
Yes, historically they had one chance to invade Africa.
and if Agothacles is dead and/or they lose the PC marker in Africa... then they can never go back?
Correct. Once they are kicked out of Africa that is it.