1. I do 3 tower stacks. I'm running three summoners, two with hunt + monk guardian buffing each LT stack, and one running app + hunt guardian buffing the DST stack. 

2. Minion wall there is to prevent weird ogres pathing during the last couple waves. Sometimes the ogres will take a weird path and get stuck on the east core. If that happens and you dont kill the ogre fast enough, he can take a swing at the core. You could not build any minions there, or maybe just a spider, and it will probably work most of the time. I just decide to build a bit more so I can afk more consistently.  

Aura placement might vary slightly depending on your range stat. Auras need to fit into the buff beam after your monk guardian buffs them into the buff. I also rate bug the electric aura so they deal extra dps. You dont have to move your hunt guard summoner outside on the west side to buff auras, just head to point 3 in the corner, it will get the auras from inside. 

You can block both entraces marked by point 4 with minions if you have very low stats and ogres can get to your towers. 

You want to be all summoners from wave 23 until the end. You shouldn't need to upgrade minions but you can if you want. I personally only upgrade auras and towers.