Need opinions/advices/suggestions.
Some of that course might be vaguely useful for background information, but, if it is for Moodle 1.8, much of it will be useless for developing against Moodle 2.0+ (never mind Moodle 3.0+).
As it says in the link at the top, the Moodle dev docs are a much better starting point, as is Tim Hunt's introduction at: http://aosabook.org/en/moodle.html
Well, some of the directory structure stuff is still valid (e.g. blocks are still found in 'blocks/', activities are still found in 'mod/', capabilities + DB structures are still found in 'myplugin/db'), but not all of it is correct (e.g. language files go in 'myplugin/lang/en' not 'myplugin/lang/en_utf8', there are many new files that go in 'myplugin/db').
In addition, the database API, files API and logging API have all completely changed; automatic class loading is strongly encouraged, instead of using locallib.php; the context API has changed.