What is the best approach for many routes / pages and self-made template in Flutter, for mobile?

• I started to build an app in Android Studio using Flutter (Dart). I
  want to insert into the app a summary of the two books, so one it will have
  35 routes (or pages) and the other another 35 routes (or pages).
• At this moment my app looks like this: I have a Intro_Page with a
  button that routes to the Main_Page. From the Main_Page there are
  two buttons: one for BookA, the other for BookB. After entering the BookA the user, after the text, will find another
  button to the next page, BookA_1 and on this page another button
  to BookA_2 etc.

My question are:

1. Is there any way to use a template that can be reused for each page?

2. I have to put all the code into the main.dart file or I can make a dart file for each page and navigate between them with
   buttons?

3. Is there any possible way to create a self-made template that it uses the design layout in all the pages so I don't have to rewrite the code for
   one of each? Just the layout not the content (the text).

4. Is there any other better way to do this?

PS: Any other suggestion will be helpful.

Thank you very much if you answer this question!

You can create one generic class for routing, in that you can just reduce the navigation code.

You can create one class like this

import 'package:flutter/material.dart';

class MyNavigator {
  static navigate({BuildContext context, Widget page}) async {
    await Navigator.of(context).push(
      MaterialPageRoute(builder: (_) {
        return page;
      }),
    );
  }
}

And use it as

MyNavigator.navigate(context: context, page: BookA());

I hope it will help you.

------------------------------------ UPDATE ---------------------------------

Also you can use extension methods as well.

> For this to work, you'll need Dart 2.7 minimum!

Implementation for extension method is as follows

import 'package:flutter/material.dart';

extension NavigatorHelper on Widget {
  goHere(BuildContext context) async {
    await Navigator.of(context).push(
      MaterialPageRoute(builder: (_) => this),
    );
  }
}

And you can use it as

BookA().goHere(context);

In my opinion extension method is good way.
You can use both.