Hi dhcsim,
Yes Cathe's step is 16 inch on that one, but you can use your 14, or even lower. If you don't mind, here is a bit of advice I always tell clients: Try it once on a lower level and see how it feels, and then move it up to an appropriate level. This will give you the gage to say well 8 wasn't enough but 12 would be too much, etc. So you have an idea where to start basically. As the best workout is the one custom for you. And the workout won't kill you the first time around, so if anything tricky comes up that looked really easy the day before when you watched it, your on a lower step, which makes it easier to master. So the next time you can keep right along with Cathe, rather then still have a problem with the tricky part. It's always awesome if you got the muscle to jump right in with Cathe, too. But it's always less injury prone the first time around to take it easy. Always use what is appropriate to you. If you've never did 14" then don't start a new workout with that. Especially one of Cathe's, you maybe to get away with it from another instructor, but that's just suicide with Cathe.
THe plate vs dumbell really depends on the person, some people feel that the dumbell is easier to blance as it has weight on both ends, where as other feel it's easier with the plate as all the weight is centered in one spot. I personally like the plate better, for me having all the weight in one spot, just is easier, and I personally have much more balance with it.
HTH,
Kit