You can just upload your files to the server and they should work just fine with a very few exceptions.
The server compatibility you are seeing is for scripts run from a schedule in FileMaker. As an example, we have a script that Server runs for us late each night to do certain maintenance chores.
Where you may see a difference when you put your files up on the network is with global fields. When you modify a global field from a single user file, the changes you made are retained when you close the file. When you are a guest of a hosted file, you do not see any changes made to a global field by another user and any changes you make are not retained. Instead the value of global fields revert to the values they were given the last time the value was modified from the host machine. (Note server schedule performed scripts can modify a global field value and then the change is retained as server schedules run on the host.)
That's great news.
So getting the server version for security, backup and speed is a good descision?
The "Pause / resume script" that scared me most about not being compatible in server won't be a problem when used in the client applications in a split external data source on the shared network drive?
Pause/Resume won't be a problem.
With any upgrade decision, it's a cost benefit analysis that only you (or your boss) can make. You gain a lot, but it costs a lot of money also.