Welcome to the community!
As to your question about potting slipper orchids: Instead of a plain bark, we mix the following together, wash it completely, let it soak overnight and then pot up the orchid:
Small Redwood Bark
Perlite (sponge rock)
Charcoal (the size of the redwood bark)
a small amount of coconut husk (small and sometimes medium depending on if it is a paph or a phrag)
And in the bottom of the pot before any of the mix goes into the pot - we place two or three of the packing peanuts to make sure there is plenty of air exchange around the roots.
Orchid potting is based largely on your (the grower's) watering habits. If you don't water very often, you will need a mix that holds more moisture. If you love to water your plants, then you need a mix with larger pieces that drains quickly so it allows the roots to dry out before you water again.
Finally, remember to flush the bark mix well at least once a month to make sure your are removing any salts left over from your fertilizer.
cheers and welcome to OrchidTalk,
BD