i also entered the temple at level 12, but i havent been any further in broken valley than a cutscene at the quarry area.
i found the black ring soldiers near there quite hard so i left and went towards maxos.
im past the first shrine, and have entered the eternal maze so i cant go back to broken valley yet because there isnt a teleport shrine anywhere in site and i dont think i can go back the way i came to the first one.
as for the enemies. the skeletons in armour werent that hard, i find that creature you can summon works wonders as a decoy for their attacks, although hes useless in the eternal maze because he always gets trapped behind doors when they close.