Hi,
There is a really good web page for Coelogyne culture here :
Cool-Growing Coelogyne Culture
I am far from being an expert with Coelogyne. I have C. cristata (growing in S/H, bloomed for christmas, now 3 new growths) and C. nitida (currently being rescued in live sphagnum). I had troubles with these plants because I wanted to transplant them just when I got them, they were not actively growing and they really did not like being repotted!!!
The question you have to ask yourself is : do I really need to repot ? Is your plant in a very tight pot or can it wait a year, so this year it could get to "know your place" and "feel at home" before you repot...
But if you really cannot wait to repot (I know it is hard
), from my little experience and the reading I've been doing on-line:
1. The best time to repot is when the plant is starting new growths and new roots
2. The new pot should not be more than 1/3 bigger than the previous one. If you pot is too big, you'll have trouble with the watering...
3. The best way not to disturb is to take the entire plant+medium (just remove gently the pot or cut it) and put it all in the new pot (with a bit if new medium at the bottom), then fill with your medium
4. A corse medium seems to be best for this Coelogyne, something with fine and medium bark, some perlite, some charcoal and some chopped sphagnum. But it depends on your growing conditions and also what medium you prefer...
I have my C.cristata in hydroponic pellets (hydroton) with a layer of live sphagnum on top. The pot is sitting in 2 cm of water (so the part with the hydrotton stay very moist all the time)
Good luck, I hope you'll find other Coelogyne growers to help you...