personally, i would just use coal or coco husks as potting medium for any orchids. I find
that spagnum moss stays wet for too long and the roots gets rotted... but thats me
because i water every day. Maybe you can get away with spagnum moss if you just water
1x a week or so. As for Vanda I love to just hang them bare root, provided that they get
enough humidity, if not, potting them up would be a good idea. I bet somebody more
experienced will be able to give you better advice.