Glad to hear you're able to log in again.
Yes, simple deleting the folder is not a good thing. You should uninstal it. But if you perform the installation again (before uninstal) it might break your website again because some of the configuration data are being kept in the database. Here has more information you may need:
This plugin is a good one, actually you may use it without causing the 500 errors. Don't enable the features you don't need in this plugin. Some of them requires lots memory. So far what I know are File Change Detection and Backup. Try to disable them, this plugin is great perhaps you may love it too.