So let's talk numbers. 400 Antminer s9s will require 48,000 CFM of exhaust for proper cooling in warm environments. You should do five 10,000 CFM fans. They key is to be able to turn off individual fans to lower your CFM when days are cooler. You NEVER want to assume pushing a lot of air is a good thing for the miners. Too much air can cause the fan guards to get too cool and build condensation. This will lead to corrosion on the heat sinks. Typically for this amount of miners, you should also include a fan that can re-inject the hot exhaust air back into the cold isle. You will want to do this in the winter and keep the "cold" isle around a constant 80 degrees F. There are automatic systems that can be designed to do all of this for you.
Great information. I would give consideration to putting 1 of the 5 fans on a VFD (variable frequency drive). In the long run this helps save energy by helping you when yourself "between fans". Instead of 1 running full out it will adjust from say 25 - 100% capacity reducing your power consumption. The other 4 fans can be set by the PLC to turn them on and off in sequence.
This may also be useful in the Winter months as the fan on VFD can still move the amount of air required and not more than necessary. (Can't say I'm familiar with Texas winters so I don't know how much more planning you would require.