Sorry, cant tell you something about that... I didnt activated it yet and dont want to since I dont know how T-Mobile handles Sim-Reactivation (in case my Fire Phone stops working).
I think I'll just test it for some time now whithout Sim and maybe (one day) I activate it
Yeah, that's also my point where I got stuck ^^
I like the handling of fire OS without this bottom bar.
I just configured Nova-Launcher that the lower Button takes the place of a Homebutton and a swipe from beneath-screen to mid-screen is 'back'. Works perfectly for me ^^