Key differences between the design system and the style guide and UI Kit:
UI-kit and guideline are products, and the design system is a methodology;
UI-kit is assembled after the completion of the project design;
A design system is created when at least one project is completed, and there is data for analysis;
If you have few pages and content, you can limit yourself to the UI-kit, and in other cases, you should register the behavior of elements and project rules in the guideline;
When working with several projects under one brand design, you will need your design system to unify and simplify work in the future.