The error “Uncaught TypeError: undefined is not a function” is in the file wp-content/plugins/js_composer/assets/js/js_composer_front.js (line 236).
Try to replace the code as you said.
Let us know if you need more help.
404 error means you don’t have custom.css file. Here you can watch the tutorial how to create it.
“Uncaught SyntaxError” means you’ve made some syntax error in the code. Please check it more carefully.
In this case we recommend you to create a ticket at http://support.8theme.com/ and our specialists will look into this issue more deeply. Don’t forget to provide your credentials to FTP and wp-admin panel in the ticket.