Grant, a little background. But first the biggest choice you need to make when deciding on a KitchenAid is tilt head or lift bowl design. People who bake but don't do heavy doughs and such seem to prefer tilt head. Example: Not long ago I had to do a rebuild for a commercial cookie operation. It was all they did. Cookie batters and doughs are lightweight and require frequent stops to scrape down the bowl. While I was rebuilding the machine, I loaned them a 6qt lift bowl. They hated it. Why? Because it was a little more difficult to scrape the bowl down. However, when it comes to heavier doughs. while a tilt head "can" do them they are not nearly as efficient or as strong at doing them. Main reason(s). Tilt head uses a screw lock on the bowl. Heavy doughs (bread, pizza, bagel, etc) can unseat the bowl and even damage the locking mechanism on both the bowl (base) and in the head of the machine. Reason is once the bowl is "locked" on the lift design "it's LOCKED" on 3 points all solidly anchored to the frame of the machine. Also they can use a more efficient dough hook. Most lift bowl machines use a spiral hook while using a spiral on a tilt head would tear the machine apart.
The motor thing also is confusing. ALL KA mixers use a DC motor. The reason is that going WAY back when Hobart first introduced the brand and rural America was being "electrified" they had to come up with a design that could work on DC or AC. Nowadays that is not necessary and none of the machines will run on DC supply. BUT, the motors are all DC motors. Where the differences lie is on some, they use a series wound universal motor and others use a permanent magnet motor.
Re sizes. Don't pay too much attention there especially in tilt head. 5qt is about the largest conceivable you can do. Again due to the locking limitation. Most everything else is simply there for them to hit various price points for different outlets.
You are more than welcome to respond if you want more in depth. You will see/hear things like YouTube pundits going on about how the "new ones" are made in China and use plastic. Please don't believe that nonsense. All but the baby ones are still built in Troy Ohio and still even nearly all internal parts as well are made in USA.
I could go into far more depth for you but, not knowing your own needs it would help to know what you want it to do
