These are good questions.
I didn't want to get into the details too much because I'm open to suggestions.
Whatever will get the prototype done the fastest is really the answer. Reader type doesn't matter as much as it works. Ideally, it would be able to scan the smaller button type rfid tags like this:http://www.alpha-crucis.com/en/sensors/1681-rfid-button-16mm-125khz-3700386694172.html
I suppose 125kHz is fine. These tags are fine with most of the readers from sparkfun.com.
Since this is for demo purposes only I can just unplug the battery to turn it off. A power button or reset switch for the reader would be nice, and a timeout would be better, but not needed. Ideally, I would be able to turn it on, receive a "ready" message from the screen, initiate a scan, see the readout on the screen, scan another object, see the readout, scan another, etc..