That is all correct. The power source depicted is a power bank, but it could be any 5V/2A or 5V/1A supply. The tablet is an Amazon product, the Fire HDX, wifi only version with android backbone, modified by Amazon, but it could be any android device. The screen depicts the downloads folder and the process of transferring a tcx file to the Garmin device. The internet signal depicted on the tablet is the Tripmate Nano local wifi.

Also, I don't know of a way to edit gpx files offline. Using Osmand offline with your phone mounted on the bike, you could ride part of a pre-planned gpx track, then easily add some new waypoints on the fly and navigate to them before returning to your planned route. Although a gpx track remains depicted on the Osmand map screen, to my knowledge, you can't actually connect a new series of waypoints to a gpx track; however, it's pretty easy to start back onto your track after plotting a diversion. Just long press anywhere onto your track and go. I've used that feature while on vacation in Athens recently.