Note1: 5 Lightning Tower and the Buff Beam is 5DU. This is where the main Spot is, i would recommend a Monk with Tower Boost or a Summoner with guardians to fasten up the Build.
Note2: 3 Lightning Tower and the Buff Beam is 4DU. Upgrade the Buff Beam to 3 Stars and you can ignore this place.
Upgrade the second Buff Beam to level 2 before starting the first wave.
Stats should be around 3-4k on Apprentice and Monk.