I would also recommend Remote Desktop aswell. Then all the files are stored on the Server and people cant 'forget' to upload.
Just bare in mind that if it is a legal firm then they will want good security.
If you are considering a VPN then I would set it up on the router and not the Server. Doing it this way means all the routing is done by the router and there will be less strain on the Server.
have you considered hosted exchange for emails? Its quite cheap now and would be well backed up. Plus it comes with all the lovely features of Exchange like calendar sharing etc.