This could end up being slower or faster ofc, depending how fast you build and how your stats are exactly.

Black arrows indicate DST angles.

Only upgrades needed are buff and the physical beam (at least partially). Some Divine on your EV helps (although not needed).

A couple things to note:

1) Downsize ensnare aura to the point where it barely covers the stairs, so that it will not overlap the spawns when buffed. Might need some messing around the first time you do it, since it depends on your aura range stat as to how much you need to downsize it exactly. Basically, if you end up with mainly ogres at the very end of the wave, you did it good enough.

2) Make sure the Etherial Spike Trap is far enough up the stairs, so that it's visible completely at the very top. This is a countermeasure to Kobolds, which is the greatest threat and source of damage to the top wall. If unlucky, you might need to repair the wall at the start of a wave occasionally. This is fairly rare though with correct wall placement (right where the "steps" of the stairs end, essentially).

3) The bowling ball turrets should both face down the stairs of course. You can have one of them face the bottom spawn directly and another one facing slightly further out for more coverage.

4) For the first three waves, keep only one Monk in to boost. Towards the end you might get unlucky with spawns and lose your boost for the last couple ogres. In that case, the spider queen minion should make sure ogres on the bottom of the stairs die a bit quicker at least. For more safety, run with two monks, but this will result in longer runtime of course.

5) Add a second Booster Monk, a dmg+rate summoner and your apprentice for last wave, or something similar at least. Could also add a second boost summoner with range+rate for the lightning towers. Up to you. Initiate boost would be counterproductive as the ensnare is sized perfectly for no IB. Hence you would drag out the wave unneccessarily. 

Good luck!

PS: If you would rather double boost constantly, then you can remove the Darkness Trap, the Gas trap on the towers as well as the south facing DST and add two more LTs to the mix. In addition to that, move the strength drain next to the forge and adjust the ensnare's size accordingly (so it barely reaches the spawns on the top and bottom of stairs when IB is on). Just keep in mind that you're almost doubling enemy count if you add two ini boosters. From my experience, this will only require more time and effort.