1200 S15's.
That's a lot of gear, the proper thing to do here would be hiring a professional straight away, don't get me wrong, you may get some good advice on forum, but for such a huge project, you should really just make use of the downtime and get a specialized company to take care of the cooling for you , the fact that you had to set low power mode and stop mining when temps are above 33c tells me that your cooling is terrible, I don't have quarter the gears you have but I managed to make it throughout the summer where temps can get above 40-45c ( that's over 113f ).
You could use a temperature controller module such as this one
https://www.amazon.com/Temperature-Controller-Display-Thermostat-Waterproof/dp/B07H2X4NNR/ref=sr_1_31?keywords=temperature+sensor+relay&qid=1574123185&sr=8-31Say you have 50 fans in total , run 10 of them direct 24/7 , use a temperature controller on a contactor that controls the MCB of say 10 fans, and set the temp to say 28c , another set of 10 fans on 30c and so on , this way you get to save on power and fan's lifespan, this is just an idea i know people use in other fields aside from mining, it's efficient and pretty cheap to set up , so you might consider it , as for all the other small details , again , hire a professional.