A:AnswerYes an app must be installed as part of the set routine. You don't need to use the app afterwards though, unless you are changing, adding, deleting, devices or routines or trouble shooting.
A:AnswerThe Echo Dot IS an Alexa control device. No you do not need anything else to ask questions just a network connection. It will play music from the limited library of songs it has. If you want to control other devices they must be Alexa enabled or you must purchase Alexa enabled smart plugs to turn them on/off, set timers, dimming.
A:AnswerI have 2 hooked up but I know they support each other good. I would try & get warranty so you could return them if they don’t do what you want!
A:AnswerI would get 2. I bought 2 as a gift for someone with the same sqft, and there's one in the bedroom and one located between the kitchen and the living room. If, for some reason, you use Alexa in the bathroom, then get 3.