Personally, If i was you and wanted to get the most amount of work done, with having the smallest knowledge base I would stick to a CMS. It definitely allows you to get things done that even if you spent 2 years learning, you still wouldn't understand (trust me i've been doing it for 4 and there things I still haven't figured out about some CMS's).
So for the first part of your question, yes I would spend your time learning the how-to's of a specific cms, although don't be afraid to try and pick up some basic languages such as HTML, JS, CSS, MySQL and PHP. Most public CMS's are based off of a AMP model (standing for Apache, MySql, PHP) and if you want to manipulate certain features of your site, understanding those 5 languages will be your key. The most important of those languages (and the simplest) would be HTML and CSS, those are your true keys for manipulating the appearance of your site.
With all that in mind, my personal fav is Wordpress, great support, a big community to help you, and tons of open source themes and plugins.