Any highly experienced game devs here please?

Are you guys using your original game designs or you just credit other people's works?

I'm assuming you are talking about art. Art is the heart and identity of most games. It is best to make your own, or have a person or team to create graphics under your direction.

Smart use of pre-built assets can possibly lead to great results (PUBG), but usually will look like junk, even if the original art was high quality (PUBG arguably also looks like junk). It would be pretty rare to find assets from a single artist that would cover all your needs, so you would have to mix and match, and then the lack of cohesive art direction becomes pretty obvious.

If you don't have the resources to make original art, then obviously you'll have to make do with whatever you can get.

I recall a few years back digging through the files for Eve Online. One file I found was thousands of lines of text and it was all the credits given for the libraries they used to create their code. Much of the music in the game when it first came out was also a case of being public domain licenses. Any time you can use a free resource without compromising your standards, why not? Locating resources like that isn't difficult. Audionautix.com has some great music that you can use. And YouTube has music and sound effects you can add to your game. There are plugins here that you can use and there's a lot of JS scripts out there that you can plug in to make your project really unique.

But I am going to agree with oosyrag when he says that the visual aspect of your game is it's heart and soul. If you're creating your first game sure, just use whatever works and doesn't cost you anything. But, when you're ready to take on the public, first impressions are lasting impressions. You'll have to decide which public assets you can get away with re-using and which you're going to want to be unique.