I bought the leather Apple case and will use it every now and then. I do the same thing with all of my other iPhones.
I don't see the point in buying AppleCare because if you plan on upgrading every year there is literally no reason to have it. You get one year of care from Apple, and the extension would only matter if you plan to keep it longer.
This time around I do see the 6 Plus as a two year phone, but if something were to happen to it after year 1 and before year 2, I would just upgrade and get the 6S Plus
. $100 for AppleCare is just a waste IMO. (when the phone is $200-$400
.