According to the rules we need to submit the source code for review.  So, should we give link to the source code in the game page? Or do we need to submit it somewhere else. And also should we just give the Assets folder or do we have to provide the entire Unity Project?

Hello. 

While submitting your game, you will find a field to input your source code repository link.  You can add the link on your game page as well.

You have to provide the complete Unity Project in the repository.