So it's been a while...

[IntoRain]

Wow so many stuff to read! I really appreciate those links!

I'd say, don't worry too much about OOP for PHP, it's not really that important. OOP is an easy concept created to make stuff more logical and better organized, but not required for websites. It surprisingly works really well for pet sites (since you have many "objects" with many different attributes: pets, items, users, ...) though.
After you make a site from scratch (with database stuff too, at least creating/updating users and a login system) and look a bit into what OOP is, my advice is to work with a framework like Laravel. That is what will make you go "how did I live without this before??"

Ah, and good luck with your projects, you seem to be on the right way! I'm learning how to use HTML5 for games myself, but with the Zenva Academy free course, so let's see how that goes lol