I can tell you already at this point that if your games are not free youre not gonna make any money, the way the industry on mobile is now. Its F2P with iaps and ads. I'm making so much revenue out of free games its silly.
i played your game for 4 hours it's a sort addiction machine!
i'm going to give you some tips:
1) add a marker that "always" point out bots, possibly deactivable in the option menu
2) add more skills or bonuses, like fire damage or a zombie automatic targeting
3) add a button that force a bot to come near you in case of need
4) add a healthbar for your bot
about bugs or problems, i notice that when the player is on the ground, suffering for injuries, sometimes my bots stuck, they cannot move even if there are no zombies around, also the game, after many sessions tends to slow down but if i close the game completely and restart it, the game speed come back to normal values.
In the end, an overheating process of the my smartphone happen every time the fps decrease. Game version is 1.0.5
i use mopub with networks millenialmedia and admob, all show interstitials just well sometimes i cant see them since on my country there are none in the stash, but the fillrate seems to be good and revenue is fine.