When I took over support for a couple of plugins, I was in the same boat with thousands of code style and documentation errors. I automated fixing as much of it as I could by using the replace capability of Notepad++. When I could create a very definitive search, I turned it loose with auto replace. If I could not be absolutely definitive as to what to search for, I let it find the next and if needed, then hit the replace button and repaired them one at a time.
I also resigned myself to the fact that it was going to take a while, no matter what, so I worked an hour or two each day until I was mostly finished about a week later.