I bought the Kindle Fire HDX (7") back in November and I really like it. I previously had an Ipad 1. The price on the Kindle was too good to pass up. Btw, I noticed that they have a $30 coupon today, which makes the price $199. Coupled with Amazon Prime, the Kindle makes a lot of sense. I'm a cheapskate so I paid the lower price and agreed to get the advertising, but I have found it wasn't obtrusive at all (it's on the log in screen only) and some of the offers have been for discounted books and music that I have used (downloaded a couple of albums for $2.00 each).
As far as the case/keyboard questions - I don't know about the keyboard, but I ordered a RooCase for about $15 that shuts the kindle off when you close it, can be used in either a horizontal or vertical orientation (uses a velcro strip), and comes with a stylus that comes in handy.
http://www.amazon.com/rooCASE-Case-Amazon-All-New-Kindle/dp/B00FF31HLI/ref=pd_cp_e_3
I have used the "Mayday" button once and it worked as advertised. They answered my question quickly. It was very handy because you can ask your question without having to type it in. It just seemed more efficient.
I have RA, so I needed the smaller size for my hands. The light weight of the device far outweighs the smaller screen size for me. I took me a few days to adjust, but now it seems normal.
For me the primary reason for choosing the kindle was the promise of free content (Amazon prime and Kindle lending library), but I also liked that Amazon has stated that they are ok with people keeping their old devices and using them to obtain content. I hate that my very expensive Ipad 1, in pristine condition, is nearly a brick because I can't upgrade the operating system any more.