Where do I set the number of backups for my project in Revit?
This can be done when you Save-As your Revit project.
If you go to the Save-As, you can find this at the bottom of the Applications Menu.
When the Save As dialog box opens, click Options near the bottom right.
In the File Save Options dialog box you can set the number of backups under Maximum.
Note: The file size of the backups can be the same or similar size of the current project file. So you need to consider the space on your hard drive or server.