If your host is a VM this has been known to cause problems. If not, then you may want to start by simplifying and doing a purely command line flash (FYI, flash does take a long time when it needs to generate the image for the file system prior to sending it to the Jetson). Here is a reference to those steps:
[url]Jetpack Not able to load on TX1 - Jetson TX1 - NVIDIA Developer Forums
So far as cables go you need only the micro-B USB cable. Wired ethernet is used for package install (WiFi is not supported). Serial console is on J21, not the 6-pin J17 header…if you used J17 it won’t show anything (it goes to the camera).