The Garmin watch can pick up data from any Stryd. You can set up the watch to pick up power from just your own Stryd. This is helpful if you run with other people that also have a Stryd.
2. You can enter the ANT ID using Garmin Connect Mobile on your phone (you can do the same with Garmin Express on the computer). Select your watch, and got Activities, Apps and More -> Data fields -> Settings). Note that menu names vary a bit from watch to watch.