Recommended Plugins

For styling emails:

WP HTML Mail

For creating forms:

Gravity Forms (GF) is pretty-much the defacto forms application for WordPress, and with good reason. The Nightingale-WP theme is compatible with GF, and all your forms will be correctly styled if you use it.

To display retina images:

WP Retina 2x

This plugin detects if a retina display is being used and, if so, uses the appropriate images. All you have to do, apart from installing and activating it, is make sure you have retina-ready images (i.e. double resolution) with @2x in their file names (e.g. [email protected]) and make sure they are in the same folder as the standard images, which should have the same name as the retina images minus the @2x part (e.g. logo.png).

To control which widgets are shown on which posts/pages:

Widget Context

Using the Target by URL option, I was able to have category and tag widgets displayed where I wanted with the following logic:

/category/*
/tag/*
/evaluation-reports

To add standard blocks to the WordPress post/page editor:

Advanced Custom Fields Pro

Allows fields to be set up such as header, leading-paragraph, image, etc. and then grouped into pre-defined sets so that posts/pages contain all the necessary elements, properly styled.