As for vandas most of mine are in wood or plastic baskets with no medium. When the plant gets too big you can place the basket and all in a larger basket. Potting mediums - A mixture of orchid bark, charcoal and sponge rock is a common mix. Aliflor, sphagnum moss, rock wool, tree fern, osmunda and redwood are some mediums that can be used alone or in mixes. I you are not sure what to use, check with some of your local growers.
Most growers are more than happy to help.
If you have a local Orchid Society, attend a meeting or two and ask some questions. You may even decide to join. Use what works well for you and your orchids. Please, if you use a particular mix with good results DO NOT change just because someone tells you one medium is better than what you are using. You can get disasterous results.