03 How many approximate number of screens will your app have?
The amount of screens and the complexity of any kind of application is directly related to its features. If the app has a lot of different features which aren't logically coherent, you'll have to separate them into distinct screens. This way you get a complex app with too much screens which will affect the budget, the developers work, and the whole user experience in a negative manner.
Consider an app that signs up a user for a company's newsletter and has a few screens for various parts of information the company wants to know (personal info on one screen, living situation on another, whatever). Maybe a handful of screens. That would take some very simple layouts with some EditText/Spinners/whatever. You would just have to gather the info and make a call to a back-end API to enter the user and its information into the database. Very simple and straightforward. Not complex at all.
Now consider an app that lets you send money to other people that are using the app. You enter your bank account info on the first screen of the app. After that the user is presented with a map that shows people, in real-time, within a certain radius. Two screens yet much more complex. You would need to integrate a maps and payment SDK, need background Services/Broadcast Receivers for sending/receiving payment and location data, etc. The back-end server would be more complex too.