You do not need a license key for the Visual Composer when bundled with a theme (unless you own a standalone license for the plugin).
Updates have to be rolled out along with theme updates.
Please note:
make a backup of the Theme inside your WordPress installation folder /wp-content/themes/themename/
To update the Theme, login to ThemeForest, head over to your downloads section and re-download the theme like you did when you bought it.
Extract the zip contents, look for the extracted theme folder, and after you have all the new files upload them using FTP to the /wp-content/themes/themename/ folder overwriting the old ones (this is why it's important to backup any changes you've made to the theme files).
If you didn't make any changes to the theme files, you are free to overwrite them with the new ones without the risk of losing theme settings, pages, posts, etc, and backwards compatibility is guaranteed.
If you prefer an automatic solution, you can use the Envato Wordpress Toolkit plugin as well. Since this is a third party plugin though its usage isn't covered by regular theme support.
Useful links:
http://premium.wpmudev.org/blog/how-to-update-themeforest-themes-with-the-envato-wordpress-toolkit/
Paste this in the Advanced > Custom CSS textarea
#mgm-branding {padding: 20px 0;}
Adjust the 20px value with the one of your choice.
After importing XML demo content, you are left to organize your widgets as unfortunately wordpress importer doesn't support them.
To build your homepage demo-like, please check the default documentation > Creating the homepage
If you wish to import widgets also, I attach a
.wie file from the Widget Importer & Exporter plugin, which you can use to import some demo widgets from the live demo by installing the plugin and importing the file.
You can download it here
Note: if widgets aren't appearing on the front-end right after importing, please move to Appearance > Widgets and hit the "Save" button once for each widget.
Note 2: Please ignore any widget failing to import, as the live demo has many sidebars for all the homepages layouts, which are not needed to the end user.
The images grid auto pulls the latest three posts with a featured image set, minus the number of posts featured in slider (to avoid repetition). It's possible that you simply do not have enough posts yet!
To import the demo.xml please follow this steps:
Note: You will still need assign the menu a theme location & you’ll need to configure widgets. This is a limitation of WordPress’ import system.
Unfortunately I cannot support speed related issues as the theme is already optimized at its best, slow loading times could depend on too many factors and different setup/hostings/plugins.
From a theme prospective, make sure you enabled the built-in minifiers / unifiers in the Advanced Tab.
Perhaps you want to address this to your hosting provider as they surely can provide better insights than I.
Thank you for your understanding!