Auras on the west crystal should be right at the end of the bridge. If the auras overlap the full staircase it drains a lot of health.
On the main bridge counting from the north side of the bridge: auras on the 5th board, buff beam on the 8th board, orcs and bulwark walls go on the 4th board and 14th board
Aim the DST with the black arrow, not at the crystal.
Proximity mine and gas trap can have a reduced trigger range to deplete slower, can also use a jester to move the triggers closer to the crystal.
Some LTs can be traded for Owl Nests to help with tanky enemies. Bulwarks can be traded for EV walls or more minions.