Large Content Database

We are in the process of planning and upgrading our SharePoint 2010 environment in the few months to SharePoint 2013.  Our current  environment has several databases that exceed 200G  There are many large list and unique permissions that are starting to cause performance issues on sites.   Microsoft's recommendation is keep the content database size under 200GB, so we've decided to use a migration tool to restructure our site collections and create new databases to stay compliant.  However, there are no quotas or policies applied to any of the SharePoint 2010 content databases and I concerned that the 2010 databases will get out of control and cause major issues with our storage while we are planning our 2013 strategy. Users are actively adding new files and making updates so I can't put in read-only.  If I apply quotas, it will hamper usage?  Any ideas on the best way to manage our wild wild west 2010 farm while we are prepping and planning to go to 2013?