How can I add a filter to this to exclude files that are not published/used on any page using unified search?
Model.ResultsFiles = searchFiles.ApplyBestBets().GetResult();
Or can I exclude it in the FindInitialization file?
This blog post is a bit older, but should be pretty applicable to what you're trying to do: https://world.episerver.com/blogs/Henrik-Fransas/Dates/2014/3/Indexing-only-referenced-files-with-EPiServer-Find-75/
Thanks, but I've tried that already and didn't get that to work. I found this solution by Eric Herlitz that works great.