Welcome, Emily.
Honestly, it doesn’t look too bad. I think you’ve done well with it so far.
Concerning how to pot it up, there are two things to consider:
- What potting medium was it in?
- What types of potting media will work best for the plant in your growing conditions?
As roots grow, they “tailor” themselves on a microscopic level to function optimally in that environment. Once grown, they do not change. Change the root environment by using a different medium or growing method and the plant will start to lose its old roots and will need to replace its root system. The bigger the difference between old and new conditions, the faster the existing roots will fail.
As it was in bark, which was not too badly decomposed by the looks of the roots, that is an option, but the second question is the more important one, as you don’t want to try one thing “for now” and have to change it again later, forcing the plant to have to change its root system again.
The fertilizer formula is not critical. Orchids are very slow growers. What is important is that they get fed regularly and using very dilute solutions. If you divide 7 by the %N on the fertilizer label, the result (rounded up or down for measuring convenience) is the teaspoons per gallon to use for weekly feeding.
You might find
this article to be of value, and if you’re in a quandary about which way to go for potting, tell us more about your growing conditions and watering habits, and I’m sure you’ll get lots of possibilities!