In IPH you should download the Min Sell prices unless you intend to put up and maintain Buy orders, in which case Max Buy is better.
For a manufacturing spreadsheet what you are aiming to do is replicate what IPH does, find the current ISK/hour and other rates. When I started constructing my spreadsheet IPH didn’t do what I wanted, display a list of my Blueprints in ISK/hour order. Now it can!
However it’s no great effort to keep the spreadsheet running, so I use IPH for cross checking. If it strongly disagrees with me, most likely I’ve made a typing error. Meanwhile the spreadsheet has found other useful data to download and analyse.
One thing a spreadsheet can do well is stock control. When I’m buying it tells me exactly how much Tritanium I need to avoid annoyingly running out at the factory, and at the other end of the supply chain if there has been a sudden run on Distressed Widgets and I need to produce some more.
A helpful article about IPH: