will the small 1/8" audio connector looking thing on the USB cable work as an audio input via a 1/8" stereo plug or do I have to use the RCA aux in to provide an input?

That is a full AV input by the way. And yes, you can use it for that purpose. You will have to set the AV1 input in the settings screen to VIDEO in order to get a signal into the unit.

cool that saves me from having to use the other audio input. since that input is a full AV is it going to try to display the video from that feed also when I select it? since I would be using it for audio only I would want it to display the map while playing audio from the input.

If your device is capable of displaying an image on the screen then yes, it will.

Once you have your music playing through the aux, pressing the Mode button will take you to the navigation screen while the music plays.