[Vuejs]-How should a frontend framework (like Vue/Angular) interact with a backend MVC framework (Laravel/Sails)

You can do both i.e. keep frontend framework in Sails project as well as separate independent project.

I have done both and I keep following points in mind while making this decision:

1. If the project is complex enough then its better to create a separate project using some scaffolding tool.
2. If the project is going to change frequently and evolve on its own then also its better to create a separate project.
3. If some one time/small view is to be made then I would prefer to keep it part of Sails project

Since you are using frontend framework for admin panel which I think
will be complex, I would recommend you to create separate project on the same server.

You can use yeoman for scaffolding. I have used it for some angular projects and it works great.