When performance matters, it's best to use the right tool. If you require many joins and relationships across your schema, skip MongoDB despite your preference for a MEAN/MERN stack. This is what MongoDB says on their site: NoSQL databases are designed to handle unstructured data (e.g., texts, social media posts, video, email) which makes up much of the data that exists today. Multiple joins add up in MongoDB. You can read more about my opinion .

Becoming a true fullstack developer is difficult to accomplish. There are improvements in frameworks in libraries to aid a developer cover breadth, allowing newer developers to ramp up quickly, but it seems like there are a lot of missing pieces. I think the term fullstack is being misused a bit these days. My opinion on this subject is here What Does Being a Fullstack Developer Mean in 2017?