Dendrobium Spectabile when to repot?

[Syrinth]

Hello everyone. In April I finally got my hands on a lovely blooming size Dendrobium Spectabile. I was told that I should repot it into medium bark from the pure sphagnum that it was in but I waited until the flowers faded.

It's been a little while now and I see a new growth at the bottom of the plant. Should I repot it now, or should I wait?

Additionally, it's in a very tiny pot, so I assume that I should keep it the same size? Does it like being rootbound or should I slowly increase the pot size?

Last question: Two of the older small canes turned yellow and died. I assume that this is natural and not something to be overly freaked out about? It happened last month and I've seen no other problems, although a few leaves have turned yellow and fallen off some other canes.