I would further enhance the question by asking: What the hell are you collecting that each sensor stores 500GB in 24 hours - photos? Seriously, these aren't sensors - they're drive fillers.
Seriously, if "sensor units scattered across a couple square miles" means 10 sensors - that's 5 Terabytes to initialize and mount in 30 seconds. I suspect that the number is greater than 10 sensors because the rest of the requirements are so ridiculous.
And why the sneakernet? If they're in only a couple of square miles - why not set up a mesh network and deliver real-time data without the need for daily collection? 30 seconds to boot probably wouldn't be a requirement if the system is only booted once.
All of the questions about why this person is even involved are probably moot. He'll be outed as an idiot in short order.