Workshop (PostgreSQL): Great for structured data like users, roles, files, and comments. You need relationships and strict rules here.

Forum (MongoDB): Perfect for flexible, fast-changing data like threads and messages. NoSQL handles unstructured data well.

Now,

• Using both is okay: Since your workshop and forum are on different subdomains, they can run independently. Users can still share one account (auth system) while each app uses its own database.

• Using only PostgreSQL: You could do everything in SQL, but the forum might feel more rigid. MongoDB gives you flexibility for discussions.

According to me,

Stick with PostgreSQL for the workshop and MongoDB for the forum. It’s a solid combo, and many apps mix SQL + NoSQL for different needs. Just make sure your auth system (user login) works across both!

If keeping things simple is a priority, PostgreSQL alone can work—but MongoDB will make forum management easier.