I understand that it can be a difficult decision to make. I have just a few comments that might help you out. Ei
1. 12 people accessing one central file at the same time was creating latency, especially during sync to central and open file. By setting up a Revit Server and saving and accessing your project files on there, you shouldn't get the latency issues. We have multiple offices and this is the only way we can utilize people in different parts of the country. Revit server doesn't cost anything but you would need a good IT person to set it up.
2. Each discipline has hundreds of sheets, and several hundred views - makes for an overloaded project browser and large file, and more items to sort through in the browser. Creating discipline worksets gives you the ability to open a project and specify which worksets you want to load. The views and sheets will still load but not equipment, piping, etc.
3. Do not want an electrical engineer to accidentally delete a mechanical unit, or upgrade a central file. We are dealing with different skill levels. Not much you can do about that.
4. Our template would be easier to manage as combined, but very large file size with a lot of content. Our template is about 80mb and all disciplines combined on a large 7 story hospital project the file size is 600mb. It takes a few minutes to open through revit server but once it is open we don't have any slowdown issues.
5. Some projects do not involve all disciplines. Those views sheets could be deleted when the project is first setup
I'm not trying to persuade you in any way just wanted to give you a few ideas since we are in the same type of company. Good luck