The first thing to consider is what access these staff members need to have.
If they don't really need Office User Functionality or Staff modules then simply turn that off on their user permissions (set them to "Not Required" per user from Administration->Users). That way they can't see any documents or information beyond their visits, meaning they are a support worker.
Screenshot of user permissions (below is a support worker example)
When Office User Functionality module is required
If they are an office worker (as opposed to a support worker) or if they are a Support Coordinator, because Office User Functionality needs to be enabled to make time-sheet entries in Support Coordination, then follow the instructions below. Note that even with even at the Read only level it still allows a user to view the documents.
Simply set Office User Functionality at Read only level and turn off access to the Staff module. Only administration staff should really need access to the Staff module so if they are just helping you with scheduling then this will work for you. The documents that you don't want people to see can then be uploaded into the Staff module. The result is that they can add time sheet entries or help with scheduling but cannot see any documents added under the Staff module (such as employee contracts and other sensitive documents.
Note that Admin access can still see all these hidden documents with access level which starts at "Read and write" and "Advanced" for Office User Functionality.
When Staff module access is required
If they do need to have access to the Staff module, then documents cannot be restricted because even Read only level it still allows a user to view the documents.
It would be better to get a document management system or an Intranet to manage document access.