You can find Submission and Publishing sections in the Marketplace FAQ. It should answer most of your questions. https://www.unrealengine.com/en-US/marketplace-faq
Marketplace Guidelines are available here and you should check it out too. Marketplace Guidelines - Unreal Engine
See section 2.7 (File Structure) to see how your files should organized before publishing it to the Marketplace. To answer your question - yes, you will have to provide your whole project “with all stuff and files”. Not all files are required though, it’s explained in details Marketplace Guidelines.