Hello,
Thank you very much for choosing our theme and for contacting us.
1. Your home page does not show 404 error. Your home page has this view https://gyazo.com/8edcca2c371b2575b3cad54c3477007a
2. I have managed to open the Header Builder https://gyazo.com/6540c8f36618da1595a2d765dee2a25f
3. Most likely, your website performance suffers from the content you have added to your website. It may happen in case of too many plugins, large not optimized images or other resources. So we suggest you to remove unnecessary plugins, install some kind of JS & CSS optimizing plugins like Better WordPress Minify and a caching plugin like WP Super Cache. Also, you can use GTmetrix tool to see what makes your website slow and optimize these parts of your website.
Best Regards