Managing Site With Multiple Blogs

Here's the deal, I intend to make a site, www.example.com and the different sections will simply be blogs. Since I will be the only one blogging initially, I want to know what is the best way to do a set number of blogs and build from there while keeping the content. In other words, let's say I want to do one blog that covers Movies, Music and Videogames, I could call it entertainment.example.com Let's suppose I get somoene else on board want to make videogames into its own thing, what do I do from there? I am thinking that I could simply use categories and make every post under one of the 3 tags (movies, Games, music) in addition to any other tags I want, then take the URL for the respective tags and link to that? Is there a better way to go about this?