Button installs which version of WordPress?
WordPress with MySQL: Button will install the latest version of WordPress 4.3 with MySQL.
WordPress with PostgreSQL: Button will not install the latest version of WordPress 4.3 with PostgresSQL because the plugin "PostgreSQL for WordPress (PG4WP)" is compatible only up to: 3.4.2 (See details: https://wordpress.org/plugins/postgresql-for-wordpress/) We do not have any solution for this at this point.
How do I upgrade WordPress & Plugins with the latest version?
You can get the information from the setup menu.
How my media files get uploaded on WordPress?
You can get the information from the setup menu. Goto bottom of the setup page for "AWS configuration for WordPress Media".