If your site contains a lot of user data such as images you may want to consider using a plugin that would offload that content to a 3rd party provider such as Imgur or Amazon S3. Plugins exist for NodeBB for both of those services.
That makes no sense The search plugin has nothing to do with themes or skins. Do you have any errors in your logs after you disable the plugin and restart the forum? What about when you run ./nodebb build and restart is everything working after that?