Your best bet is to use that orchid mix. Sand is a definite no-no. I don't use potting soil or african violet mix because they retain too much water. Hoyas are epiphytic plants, meaning they grow up trees in the wild and use aerial roots to attach themselves to tree trunks and branches. Because they are epiphytic, you want to try your best to provide them with the best match for their growing needs. In your case, that would be the orchid bark. It retains enough moisture to keep the plant happy, and provides great drainage, so that the roots don't stay trapped in a waterlogged environment.

The most important factor in successfully growing hoyas is to provide a light, airy, fast draining potting mix. There are exceptions - hoya multiflora, darwinii, coriacea, campanulata, sammannuana, caudata, and others prefer it a bit more moist; I grow these ones in either hydroton/growstones or add New Zealand sphagnum moss and coconut coir to the mix - but, as a rule, a fast draining, airy mix is the way to go.

Be sure to soak the orchid mix overnight in water, and rinse it the next morning before potting up. This gets rid of fine particles and dust, and also leaches out tannins that may be present in the bark chips.

If you plan on weekly feeding, don't add time release granular fertilizer to the mix. If you plan to feed over time, add 1/2 teaspoon of granular time release fertilizer for every 2 inches of pot. A 2 inch pot is 1/2 teaspoon of time release fert, a 4 inch pot is 1 teaspoon, and so on.

For weekly feeding, 1/4 tablespoon of your favorite water soluble fertilizer to a gallon of water will do. I use plain old MiracleGro water soluble tomato food as a weekly feed, but also foliar feed with FoliagePro (one to two times a week) and ProTeKt (once a month). Is it necessary to foliar feed? Dunno, but from what I am seeing, my plants seem to be thriving.

Hope this helps!