What files need to be moved for Craft3 plugins? I'm trying to get the redactor onto my site. I've successfully moved over plugins from the store and a custom plugin I created. But I did those towards the start and had migrated the entire project onto the site. I don't want to move 4,000 files over just to get one plugin to show up.

I've tried moving composer.json, composer.lock, and manually moving the specific vendor folder in as well. I also migrated the database from the dev site to the production site.
So you're really close; composer.json is a list of packages and their semvers that should be installed. composer.lock has a manifest of what is actually installed.

In order to deploy to production, you just need a step that executes composer install to install what is in the composer.lock file. Check out the Deploying Craft CMS section of this article for a more thorough run-through.