Configure a Linux setup

We need you to make a linux image that will serve for the following application: When a vehicle drives into a designated area, the wlan connection of the device on which the Linux is installed, will connect to the pre-configured AP. Via an RSYN mechanism, the device will start syncing with an RSYNC server to see if content needs to be added or removed. The device has over USB another connections that can only see the HD as a USB drive and needs to access the hard drive of the device on which the Linux is installed. You need to create a Linux distribution that has a graphical shell but is still as light as possible. The RSYNC settings and very important, the harddsik of the device should be reachable via USB. In other words, a device connected to the PC over USB, should be able to see the synced content as a USB drive/stick. Any comments, suggestions and questions are welcome.