No issues with the valve stems. I am using the T-Valve stems. That way you don't ever have to remove the sensor if you had to adjust the air in the tire.
You don't want to put the display in a saddlebag or elsewhere. You should have the unit visible so you can see it. That's the whole point of it; you want to be able to actively monitor pressure. I have mine on a homemade bracket; attached to one of the bolts under the lower M.A.D.S.T.A.D. shield. Will see if I can find a previously posted picture of it.
Also, the tires have to be moving for a little bit, before the sensors "wake up" and start sending data to the display. Sometimes it takes the length of the driveway and occasionally the one on the rear make take longer than that, But once they start communicating; it's constant monitoring while you are on the bike.