Hint 1 indicates the defenses are on the top crystal layer.
Hint 2 and 3 indicates the defenses are on the lower crystal layer.

The structures are in a place to be targetable by the ogres (so directly south against the crystal and close or against the south edge). That way they properly aggro the ogres.

You could be a tryhard and replace an Owl Nest with an Obelisk.

Equip your Guardian with a Dice or other mana generation pet.

Before the first wave, build everything but the Guardian Towers. During the wave, build the Holy Bulwark (to aggro the ogres) and at least one Owl Nest before going out to gather mana. That way you can spam Owl Nests from a distance as you gather mana. Upgrade the buff beam. Afterwards, pull out a double huntress guard pet summoner on have it AFK on the lower level chest by the Guardian towers.

I'd recommend having the following out for the final wave:

• Builder Guardian hero
• Hero* with Huntress Guard Pet
• Hero with Huntress Guard Pet
• Hero with Monk Guard Pet (for lower layer auras)

*Hero being whatever you are target farming. You don't need to have the Builder Guardian out if you want to better target farm another weapon.

Of course this build goes a lot faster if you up the towers and use a TB. I just wanted a simple, safe, and quick to make AFK build that I don't need to pay attention to.