In my experience, I've found people progress through HTML5 very well after mastering the basics on CodeCademy, and moving forward from there. Anytime that you get stuck, there's a whole Daniweb community to help you out!
Good luck - learning HTML5 is a lot of fun, it gets hard here and there, but with a bit of patience and effort, you'll quickly become an expert.
What do you mean by platform? You can think of HTML5 as a standard. HTML is simply markup and if you develop HTML5 pages, you are following rules and guidelines.
To become an expert, I would recommend getting a hold of a few books, visiting the W3C and looking at their documentation http://www.w3.org/html/wg/drafts/html/CR/, and just developing, testing, etc... You only need a browser to work with HTML5 pages. No web server is needed. No special IDE is needed either. It can all be done with a simple text editor.