Why can't I take RDBMS Database Design practices, and use for NoSQL MongoDB Database Designs?
If you want to use a relational structure, and you're thinking about doing it like this with a NoSQL system, use an RDBMS, that's what they're designed to do.

Using the right tool for the job will always result in better performance, and no-one has ever been fired for using an RDBMS where one fits instead of using a NoSQL solution where it doesn't make sense, like in a banking situation where you need 100% guaranteed consistency, not "eventual consistency".

Using relational algebra in a non-relational database will just make you replicate relational functionality in code, and I can guarantee you're not better at that than, say, SQL Server or Oracle.