There is much advice on the internet about how to care for Hoya curtisii from never let it dry out to keep it dry all the time.  I can only say what has worked for me. The plant needs a relatively small pot where it can literally live for years (Mine has been in the same 4 inch pot for 4 years!). The soil should be relatively free draining, but also have some water holding capacity.  Peat-based potting soil amended with 25% perlite should work fine.