So, you had 2 errors public_html was 777. It needs to be 750. All of the folders inside public_html need to be 755, but public_html itself is special and needs to be 750..htaccess seems to have a syntax error of some sort. I didn't actually look at it. I just renamed it to .htaccess-old and the 500 error went away. So there is something in there it doesn't like. You can debug it by commenting out one line at a time or whatever.