I was advised NOT to use a self-tapping shut-off. Install a standard shutoff with the proper 'step-down' for the water line. And be sure you don't tap into, say, an outdoor faucet or something similiar because, if you were, then if it's cold where you live, you may have shut this 'line' off and drained it already. (Or if you haven't yet, you will soon.)
One thing I'm not sure of is whether the humidifier needs to be 'hooked up' so that it 'comes on' when the blower comes on. In other words, I don't think the unit is suppose to be 'running' when the unit is off. (I wasn't ready for this job yet but since you brought it up, I might as well ask too.) I'm looking at the same 2 units you are.