I'm honored that you have enjoyed my contributions!
Your Oncidium mix should work fine. Cyms like to stay damp but do like air though they're pretty forgiving even when the mix starts to break down. I have to admit, mine get the cheap bark (small size), with some #2 perlite to lighten it up, and if I'm remiss in potting it turns to mud, which doesn't seem to faze the Cyms much. The cheapie bark has become impossible to get recently, a lot of people are going toward coconut husk chunks. (I used to use those, then the quality declined and it needed a lot of washing to get salts out. Nothing is perfect or forever). My Cyms may benefit though, I'm likely to be reduced to useing the fancy stuff (Orchiata or Kiwi Bark) that I use for the fussier plants.
Cyms are heavy feeders. I 'way under-fertilize everything, to keep the Cyms happy, they get a top dressing of time-release pellets (Nutricote or equivalent) in the spring, then they get lightly fertilized with everybody else with no additional work on my part. My Cyms live outside, get whatever temperatures Mother Nature throws at them. They get rained on, and when rain is absent, "rain" comes out of sprinklers. Watering is less frequent in winter because things don't dry out as fast, but they still stay pretty wet even when cold. So, in short, my Cyms get no special treatment and do fine... coastal California living suits them.
One more note, light... Cyms are very high-light plants. Where you live, they probably need no shading at all. Mine are under 40% shade cloth because my yard really toasts in the summer, no shade all day. So a little shading at noon in summer if it is hot is helpful but othewise, they really do like nearly full sun - aim for lime-green (NOT dark green) leaves for best flowering.
Definitely, don't need to worry about the low temperatures, they're good down to about 29 deg F without hurting flowers. Check out this from Casa de Las Orquideas (Solana Beach)
Ice
Some of those that were in bloom through this rough week were in a show 2 weeks later, none the worse for wear.