Remark 4 and the minions are build on the middle floor.
The auras are build on the corresponding core.
If you get additional defense units, you can add a slowness aura on the top core.
Upgrade the buff beams first, then towers.
You might want to use boost summoners or tower boost monk.
For campaign build auras and buff beam first and add as many towers as possible in the first build phase. Later add the remaining towers, then reflect walls, then minions.