I would recommend that you continue to use the highest resolution and the lowest compression settings. Reason for this is so that you have a high-resolution copy just in case you want to make prints. If you can shoot RAW+JEPG, then that would be a good solution.
When posting to social media, you don't need much more than about a 2MP image. Anything larger will get reduced in resolution by Facebook not to mention that Facebook will also compress the heck out of it, too. So since Facebook will apply their own edits to your images, it makes sense to have the least amount of compression. The last thing you want to do is upload an image that has already been heavily compressed (all jpegs much be compressed by definition), just to have it further compressed by Facebook. This can lead to color banding and other unwanted artifacts.
Most people who are concerned with their work being stolen from Facebook will limit the size of their images making them good enough for Facebook, but nothing else. Therefore, limit the long edge of your images to about 1,200 pixels or less.