if you need more than 50 workspaces, I would seriously consider handling that with Infrastructure-as-Code.
You could open multiple accounts (perhaps over regions) and deploy workspaces accordingly.
Having a dev/qas/prod split is a good idea, but beware that Unity has a limit of a single Unity Catalog per region, so an actual physical split is not possible (it can be achieved using permissions though, but that is not a hard split).