ASP.NET Core apps are actually straightforward console applications. In fact most of the application types you’ll run on .net core are configured in a main method in program.cs. The answer to your specific questions about mixing different services in one app will be some combination of the following links.
https://khalidabuhakmeh.com/hosting-two-aspnet-core-apps-in-...
https://docs.microsoft.com/en-us/aspnet/core/fundamentals/ho...
https://docs.microsoft.com/en-us/aspnet/core/fundamentals/ho...