Count on falling over twice, once within the first hour, and then once again once you get use to them but forget. It won't be long before clipping out will be second-nature; you won't even think about it.+1 To minimize the chances of this find a gym or Y that has a stationary bikes you can use. (They often have pedals with SPD on one side and platform on the other or put your own SPDs on.) Then you can practice getting in and out without the risk of falling. I always tell people to make their first attempt at using SPDs on grass. I didn't and wished I had.
The experience of stopping at a light and being unable to get your feet off the pedals is not to be missed.
But persevere. Before long you'll wonder how you rode without them. Use long flat bits of your touring to practice 360 degree pedaling until it becomes 2nd nature. IMO it's like skiing, a learned skill but well worth it.