I honestly don't know how the revisions feature takes the limiter into account for posts created before it has been added. But you should be good to go for any new content created.
If you want to clean out all the revisions from the database and start fresh, there's 2 ways to do this.
1. Via phpMyAdmin: if you have experience and knowledge of working in the phpmyadmin environment you can follow these steps
2. If you are not comfortable with phpmyadmin there are some plugins that can do it. I'm not overly familiar with any of them, as I go the phpmyadmin route, but from a quick search, Better Delete Revisions comes up often
Note: if you are going to do this via phpmyadmin, I would highly recommend backing up the database, a good habit to have when doing anything to the database. Just in case