For each version of ArchiCAD your firm is using, a matching version of BIM Server/BIMcloud needs to be installed to support that version.
With vbim, you are subscribing to a Windows Server hosted in the Cloud with specs to match the requirements of Graphisoft's BIM Server or BIMcloud. Multiple installations of BIM Server or BIMcloud can be installed on a single Windows Server.
To determine if your firm will require more than one Windows Server will depend on the usage of the server by your firm. Larger projects and more architects may deplete the needed resources on a single Windows Server at which point you will be advised that another instance of a Windows Server be deployed to accommodate your projects.
Our advice is to start small and expand as your firm's project's demands grow. Migrating projects and libraries in the Cloud is easy and vbim will do this for you at no extra charge.