What are the different patterns/quantity of employment according to demands of different income ranges? I don't really have that much knowledge on economics or anything, so perhaps that's something I'd find an answer if I just knew the adequate terminology.

Rephrasing/explaining my question: different income ranges have different propensities to expend ("versus" save), and somewhat different consumption patterns (quality of products and services). 

And industries working on different quality levels also probably have different numbers of employees working on it, for the same absolute amount of money. In other words, "ten dollars" may employ less people in the cheaper food industry, than in luxury organics, and, perhaps, conversely "ten dollars" may employ more people in a "cheap towels" factory than in a "luxury towels" factory.

So, in the end, we'd have something like in general, poor people employ the less number of people per dollar invested, middle-class the most, and the richer, somewhere in between. But perhaps it would be more interesting to see that actually separated in different industries as well.

So, is that something about which there is hard data/cool graphs somewhere,  or that isn't generally a matter of concern, or yet, perhaps the answer is so obvious and easily empirically verifiable that no one really cares to elaborate on that?
So the phenomena you've identified is linked to a goods being labor intensive or not. Often ``craft'' goods required high-quality labor (think watches) to be built, while lower quality goods can be made using machinery. Now farming of all kinds used to be very labor intensive, but technology has replaced most of those workers. 

So the substitutability of a worker matters a lot here and the skills that luxury goods need may be less substitutable. 

Another factor is that when the good is more expensive, cutting costs (such as labor) at the potential expensive of quality is not always a goods idea - think how often you see ``handcrafted'' or pictures of the people working on the farm on organic products.