To create a new ASP.NET Core MVC project, you would typically use an integrated development environment (IDE) like 'Visual Studio Code.' Visual Studio Code provides excellent support for ASP.NET Core development, including project templates and extensions that streamline the development process.

The project.json file was used in the early versions of ASP.NET Core (then known as ASP.NET 5), but it was replaced with the .csproj file format in .NET Core 2.0 and beyond. The project.json file defined project dependencies and configuration settings.

Custom middlewares in ASP.NET Core are created using a delegate with the signature Func. This delegate takes an HttpContext as input and returns a Task, allowing you to write custom logic to handle requests and responses in the pipeline.

To specify multiple roles using the [Authorize] attribute, you can separate them with commas inside the Roles parameter, like this: [Authorize(Roles = "Admin, Manager")]. This allows access to the action or controller for users who belong to either the "Admin" role or the "Manager" role or both.

The Separation of Concerns (SoC) is a fundamental design principle in ASP.NET Core MVC. It advocates for dividing the application into distinct and separate components, where the Model handles data, the View manages the presentation, and the Controller orchestrates the flow of data between them. This separation enhances maintainability, testability, and scalability.

Razor Layout Views in ASP.NET Core are primarily used to define the common structure or layout that multiple Razor views within your application will share. This allows you to maintain a consistent look and feel across various parts of your web application. They help separate the presentation logic from the content-specific views.

ASP.NET Core's primary advantage in this scenario is its cross-platform compatibility. It allows you to develop a web application that seamlessly runs on both Linux and Windows without the need for codebase modifications. This flexibility is especially valuable when targeting multiple platforms and ensuring a consistent user experience across them.

One of the core features of ASP.NET Core Identity is its ability to provide two-factor authentication (2FA). This adds an extra layer of security by requiring users to provide two forms of identification, typically something they know (password) and something they have (e.g., a mobile app-generated code) when logging in.

In the MVC (Model-View-Controller) design pattern, the Controller is primarily responsible for handling user input and interactions. It receives user requests, processes them, interacts with the Model to retrieve or manipulate data, and determines the appropriate View to render as a response.

The Identity middleware in ASP.NET Core primarily handles authentication. It intercepts requests to determine if a user is authenticated and provides features like cookie-based authentication, token-based authentication, and integration with external identity providers (e.g., Google, Facebook) for user login.