New module to limit the amount of menu items per menu
In a recent project, we had to provide a way to easily limit the amount of menu items for several menus separately. Drupal does not provide this functionality out of the box so we had to hit the keyboard and take care of this functionality on our own. The result is our newest contrib module Menu Item Limit.
Installing the module is easy and does not require any magic. Just drop it in your sites/all/modules/contrib/ folder with the rest of your contributed modules and activate it on the modules page.
Per default, every menu has the ability to hold unlimited amount of menu items. You can set a custom limit by editing a menu on /admin/structure/menu, i.e. the main menu. Enter any number you want greater than 0 to set a limit. Entering 0 will remove the limit.
That's pretty much it. Now you have a nice and easy way to control your menus.