Oncidium flexuosum can be grown in pots but it has a tendency to want to grow vertically rather than horizontally...which is why all mine are mounted. This Oncidium can take a good amount of light and is fairly temperature tolerant. In terms of water, I'd recommend giving it a good soaking but letting it dry out between waterings.
I bought one several years ago and it is potted. I haven't had the heart to remove it from the pot, as it is a consistant bloomer for me, so I live it alone and just add coco chips when I need to. I pretty much leave it alone, and it re-blooms for me every year.