I can't remember if this question has already been answered on the main page, and I currently can't be bothered to check. I am very sorry if it has already been answered, I'm likely just blind.

There is no rule against the re-use of any code or assets, as long as you are the legal owner, or carry a license to use anything you include in your project. Keep in mind you must have commercial use license for anything that is not your original work if you intend to ever sell your project.