Yo can do it all in FileMaker without any Apple Scripting. Create a FileMaker file and in ScriptMaker create a script called 'startup script". It performs the script step "Open". Specify a file for the step, and then click the Hosts button and navigate to the remote file you want to have open.
The script is all set. Now in Document Preferences, specify that the startup script is performed automatically when opening the file.
That's it!