Reddit mentions of Professional WordPress: Design and Development

Good news: there's no need to be scared.

It was a previous version of this tutorial from Themeshaper that got me started on WordPress myself. Like anything else, just play with it until you're comfortable.

User roles are the last thing you need to worry about. Here's the summary from the WordPress codex. I'd actually recommend reading it from bottom to top. I make clients editors at most; I've never had one insist on being an admin.

What you'll really want to focus on is learning PHP if you haven't already, and WordPress themes.

If it's a good book you're after, the best one out there I've used is Professional Wordpress: Design and Development

Edit: Although it's good to build a couple themes from scratch — meaning creating all the template files yourself to understand how they work — eventually that'll get tedious as you'll find yourself constantly adding the same elements over and over. Underscores remedies this perfectly: it basically gives you a blank theme with everything you need ready to go. It's not a framework, just a head start. Highly recommended for picking apart and experimenting — and for building themes.

Best book to get moving: http://www.amazon.com/Professional-WordPress-Development-Brad-Williams/dp/111844227X

Find a few solid plugins, download them, and then start browsing through their source code. Literally start at index.php and follow every function call to see the application flow. There are a million ways to write a plugin, but pay particular attention to ones who use standard design patterns like MVC and the like.

Read through this series of articles to see how WP bootstraps itself. Regardless of whether you'll be working on Core, it will help you understand some of the complexities and might even be useful when debugging.

• http://theme.fm/2011/09/wordpress-internals-how-wordpress-boots-up-2315/
  
• http://theme.fm/2011/09/wordpress-internals-how-wordpress-boots-up-part-2-2437/
  
• http://theme.fm/2011/10/wordpress-internals-how-wordpress-boots-up-part-3-2673/
  
  Read up about Hooks, Actions, and Filters and try using them. For fun, do a default setup and use the 2012 theme or the like. Then make a child theme, and see just how much you can modify content-wise across the site strictly with action/filter functions defined in the child theme's functions.php file. I.E. don't modify any template parts or other .php files except functions. For starters try inserting content above common template tag calls: i.e. use "the_content" action to stick some additional information before/after the content of every post across the site. Then see if you can figure out how to modify the output of a wp_nav_menu call. Continue on from there.
  
  Here's a pretty good article for the business/personal/social skills side of things: http://www.smashingmagazine.com/2012/08/23/how-to-become-a-top-wordpress-developer/

If he/she is serious about wordpress development, at some point or another this book will come in handy:

http://www.amazon.com/Professional-WordPress-Development-Brad-Williams/dp/111844227X/

Not trying to be mean, but it sounds like you're in over your head. Seriously, if the site needs to be completed any time soon, I'd recommend outsourcing it, or advising the client to go a different route.

If you weren't given a design, and could jam whatever they wanted into an existing theme, then your "little HTML & CSS knowledge" would probably suffice. You're talking about building a custom theme. You need to know some PHP. You need to know how the WordPress templating system works. You need to be able to set up an SQL database.

Luckily, WordPress has some great documentation: http://codex.wordpress.org/ but it sounds like you won't have the time to learn WordPress properly. If you are serious about WordPress, and would like to get a firm grasp of it at some point (and I think you should, it's very popular and useful), you can check out this book: http://www.amazon.com/Professional-WordPress-Development-Brad-Williams/dp/111844227X/ref=sr_1_5?ie=UTF8&qid=1409097469&sr=8-5&keywords=wordpress

EDIT: Also, check out /r/wordpress

I believe there is specifically a book called "Professional WordPress Design and Development" that goes over PHP's implementation on the back end. I've read it, and it is an excellent book.
https://www.amazon.com/Professional-WordPress-Development-Brad-Williams/dp/111844227X

I'm going through the process of diving deep into wordpress and so far the best resource that I've found that delves into the specifics of using wordpress as a dev is this book. it should save you a lot of googling time.

Are you talking about reading up on how to develop for WordPress? If so, the links provided by others are a great starting place. I'd also recommending checking out "Professional WordPress" by Brad Williams:
http://www.amazon.com/Professional-WordPress-Development-Brad-Williams/dp/111844227X/ref=sr_1_1?ie=UTF8&qid=1414536372&sr=8-1&keywords=professional+wordpress

It's almost two years old now, so some of the information may be dated, but most of it will still be relevant.

Sounds like you're looking for something like this. I bought it and it's really good, but really the best way to learn is to figure out what you want to make, and then figure out how to make it by Googling. If you really want to learn Wordpress in the thorough way you're describing, I'd have thought you'd want to start with PHP.

This one is great for where you're at: http://www.amazon.com/Professional-WordPress-Development-Brad-Williams/dp/111844227X