SWEET! You are well on your way. HTML became XHTML, which makes it XML... sorta. lol XML is a common framework for building UIs, even when it's not HTML (e.g., Coldfusion).Don't know what I'm doing yet, but the UI is just XML so no big deal. Your trading app does look slick!
There's an app for that and what I did in my test was a call to a restful API.
RESTful is the way to go. Web Sockets for real-time streaming. But, worry about that later. You need to learn how to create and consume REST web services first. If you just learn how to create UI that consumes them, it opens a huge world, as nearly all major API providers expose their interfaces with REST (e.g., Amazon, Google, Twitter, Facebook).