1: You shouldn't be using bootstrap, even though you can with angular.

2: What do you need to do in the front end that can't be accomplished the 'angular way'? I'm not sure you understand what monolithic really means. The beauty part of angular is that you can use it as little or as much as you'd like in your web applications.

3: Angular 2 is going to be preeeetty much only ecma6. Also, understanding angular means you understand AMD, digest cycles, etc... totally applicable to other frameworks.

4: What are you even talking about?