Ask HN: How should I start on a social campus food website?

If you have all the features laid out you should start building a prototype of the service. Seeing the basic features start to come together is great inspiration to keep building and improving the site.

As for the project, you've already done some of the right first steps with the feature list and paper mockups. Building it comes next.

Pick a couple of features to build out and maybe select a single university/town to focus on initially and build out functionality and content for that first.