You can ensure that all of your logs are on "warnings". Type show logging level verbose to ensure that they are. That might cut down on the messages.
In terms of the upgrade, if you told me that you had one controller and you were scheduling an upgrade anyway over the holiday, and you had an upgrade and backout plan, I would say yes.
Not knowing the details of your network, I would say that it is not worth it.
If you want to upgrade you can certainly upgrade all the controllers then reboot them at the same time and philosophically, you would be okay. The discovery method your access points use, the bandwidth they have to the controller and the method you use to monitor the state of all of your APs across those 12 controllers would dictate how you manage such an upgrade. If you have never done this before, it is not a good time to do so without a plan, regardless.