Designing your CE3 Theme for WordPress is pretty straight-forward, especially if you're already familiar with using the CE3 framework. The most important thing you need to know about is this, located in the Color Palette control pane:
These controls allow you to change what is visible in Lightroom's Web preview, so that you can customize various types of content for your theme.
Preview Content Type
Changes the Web preview to display various examples of content that might appear on a WordPress blog, such as post excerpts on the blog's front page, a full article view, images in posts, comments threads, etc.
Allows you to preview either the one-column or two-column layouts for each view. Preview and configure both views; you are not committing to either a one-column or two-column layout here in Lightroom. The number of columns and their layout can be changed on-the-fly for each page type from within the WordPress admin area, so you'll just want to use these options for design purposes.
Sets the spacing between the main and sidebar content areas in the two-column layouts.
Primary Content Position
In the two-column layouts, allows you to preview the layout with the sidebar on the left or right side. Again, you're not committing to a layout here in Lightroom; this is for preview and design purposes only.
Primary Content Width
Sets the width of the main content area in the two-column layouts, with the sidebar taking up the slack. Widths are relative and fluid, so will vary depending on the width of the browser view.