So, I have 21 engineers now, and didn't totally understand what they did. Based on perusing around, it looks like you can assign each one to produce certain resources. Am I right? If so, how do I do it? I can't find the option.
You can assign Engineers in the Workshop tab.
You have to realize most things are utterly useless for Engineers to make, because you can just click the "all" link at the left to make a ton. The Engineers make the item one at a time (multiplied by craft bonuses).
As per the screenshot, Kerosene and Compendiums seems to be the most useful things to make, because they take a ton of resources, you can generate a ton of said resource, but your cap for said resource are relatively low, and you need a ton of them.