Sphagnum moss can be a little controversial. Some of use it with good results (Gilda grows in it, or at least she used to, and wins ribbons) while some swear by bark. As your collection starts to grow and you acquire orchids that are potted in both types of medium you will get a better feel for which one suits your growing conditions. If you do decide to repot in moss instead of switching to bark, make sure to pack it loosely and you should be fine. Also, you might want to put some stryofoam peanuts in the bottom of the pot. They seem to help drainage and create some air pockets.