What type of treadmill should I get?

They are very boring to use, so I suggest before you make that purchase, go to a gym or running store that has one you can try out (just for the experience). Most of them are electric so will run on their own. I picked up a real basic one off a Facebook buy/sell group a few years ago for $50. I didn't need anything fancy and this one doesn't tell you what your pace is (there's just a slider you move to go faster or slower). 

Make sure it's what you really want, because they typically retain for several hundred dollars (or more) and take up a lot of space. I don't use mine often, but I have a room dedicated to exercise equipment so it's out of my way and I didn't spend much on it so I don't feel bad about using it a handful of times a year (because I prefer running outdoors).

You can get a motorised treadmill. It's very good.

None! You'll probably break it! Fatass!