Choice of media is a choice based on lot of factors ( watering frequency, relative humidity, your grow area micro climate). Choice of media just one the factors in orchid growing. Given that you have about 180 plants, you can try a similar looking phals may be 2-3 in organic and inorganic and observe them and then decide what works in your environment.
Coming to coarse, medium and fine media. I use same media for all my Orchids and they seem to be doing ok.