On the subject of "choosing what to read next"--you left off any questions about store loyalty or aversion. Some people are always going to choose something from Amazon. Some won't ever choose Amazon. This *drastically* changes how they choose.
I don't do DRM; that means I don't get Amazon or B&N ebooks--so I don't get much of a "you may also like" selection. I do read a lot of Smashwords, but it's mostly by random browsing and collecting books when they're on sale, and deciding later what to read.
Also missing from your survey: any acknowledgement that "what books do you purchase/download" might be very, very different from "what are you going to read next?" I purchase when I have money or books are on sale. I might read that book much, much later.
Not sure that's a problem; you should just be aware, when you're writing up your thesis, that your survey didn't differentiate well between acquiring books and reading them. You asked about how people acquired books; what they actually read might be very different.
How I choose what to *read* next usually involves crawling through my "purchased ebooks" folder, or heading to AO3 and downloading whatever
novel-length Avengers fics have been finished recently.