List of what to learn

PHP
MySql
How to use themes
How to use plugins
How to develop themes
How to develop plugins
How to customise the MySQL Database
How to add a wordpress blog to an existing site
how to add a wordpress e-commerce shop to an existing site

WordPress developer training courses:
http://wordpressdevelopernetwork.org/wordpress-training-hertfordshire/
http://www.manta9.com/
http://www.ntileeds.co.uk/training/wordpress-developer
http://webdesign.com/

php course
http://www.php.net/manual/en/tutorial.php
http://adambrown.info/b/widgets/easy-php-tutorial-for-wordpress-users/
http://www.siteground.com/tutorials/wordpress/wordpress_create_theme.htm