If you want a complex relationship between databases that work best when they are all opened need FileMaker Server and that pretty much is the purpose of Server. It makes databases Available all the time securely. Plus you can run schedule scripts that do the importing so that if they take a long time, they don't lock you out of using your FileMaker Pro client. Not to mention Server does many other things like live backups (Server automatically pauses databases without having to close them). Just something to think about. Best of luck!