That oak tree has a massive staghorn resting in its crutch already, Patty. To be honest, I don't want to put anything more on that branch until the little Encyclias take hold. If I put a brom or a stag above them, it would cause more shade. They need all the light and water they can get, right there and even though now the sun is high enough to reach them, in winter they're in full shade.
Once I'm sure of them, I think another orchid will go in the elbow of that branch but I'll mount it slightly over the other side so it tends to grow and cascade down the side away from the Encyclias. What do you think, a big Laelia or something?
Those wood rounds are lovely, but I'd leave them out in the weather for a few months before using them. Do you know what kind of wood they are? If they were something like pine, you want the aromatic oils to wash/bake out of them before putting an orchid on them, I think.