The config type is based on whether or not you are restoring retained information when Nagios starts. If you are unsure just leave the default value. If you can see host and service groups but not hosts or services try changing this setting.
Enable displaying host icons in the hosts grid. The icon_image and icon_image_alt parameters of the Nagios host definition are used to set the image. Icons should be 16x16 to get the best look. this setting does not affect the host status icons.
Enable displaying service icons in the services grid. The icon_image and icon_image_alt parameters of the Nagios service definition are used to set the image. Icons should be 16x16 to get the best look. This setting does not affect the service status icons.