No. Microsoft is much better at handling an ecosystem than Amazon. As far as I can tell, MS is using standard Android with Google Play Services(?) Amazon was trying to create its own ecosystem.
Amazon has a nice suite of services. A phone that has Music, Books, Shopping, Cloud Storage for Photos, and a few key apps (Uber, Lyft, popular games) but somewhat constrained otherwise, would be great for Seniors or people who don't need a high-performance general-purpose computer in their pocket.
Perhaps, but I believe that not being able to install one or two crucial apps (e.g. banking) would be a deal-breaker for a good portion of those people.
How would that be any different than what they tried with the Fire Phone? You can already buy cheap Android phones that can do all of those things using either Google’s services or Amazon services