I'd like to learn about either Drupal/Joomla and how to set up CMS websites.

Before diving in the deep end though, should I study Object Oriented
PHP programming in detail?

It's worthwhile learning about OOP but not in detail, it's quite simple to get the basics and from there it's just figuring out what will save you time in the long run.

The best way to go is making sure your 100% of the basics of programming and theories behind coding.

No you don't need to learn OOP in PHP to set up and run a CMS. The only time you may need to learn it is if you intend on diving in and customising your installation. I dont mean custom templates either. You will only need to know some html to customise a template.

Just dive in. Get a CMS set up and build your own mini website with it. Doing it is the best practice.

^^^^
agreed

use the sample code to learn the system.