Create a sitemap of all the relevant pages of your feature. You can use google drawings or omnigraffle to create an overview
Sketch some wireframes (or wireflows) of the interface. These can be rough sketches or more hi-fi. Find a fidelity that suits you.
Turn your wireflow into static HTML pages. Do a HTML breakdown of your wireframe to see which semantic HTML elements you need. Ten create the HTML page for your feature.
Add some presentational CSS. You've already done some branding research so you're already able to set-up some basic styles. Think about colors, fonts etc.
Thank you for the feedback, I updated my wiki. You can find it under "week 2, 3 and 4". I have to say, to make it more concrete, it helped me to keep a clear overview.
Start working on your interface!