Repotting Questions

[HiOrcDen]

Two orchids I bought I believe a bit over a month ago were already brimming over the pot, and now moreso. They still look very healthy.

I'm wondering if it harms Orchids if they stay too long in a pot, or if it just stops their growth, kind of like a Bonsai.

In any case, I have a couple questions about repotting. I want to figure out the medium they're planted in (also need to know, is it important or at least advisable to use the same substrate?) One of the elements is wood chips. But they are a bit soft and spongy. Is this a different kind of Orchid bark, or do they get this way after some time? The other element are these white stones. They are similar to pumice, but have a rougher surface, and break down to sandy particles. Is this some kind of white charcoal? That's my best guess.

If anyone can identify these mediums, I'd appreciate it. I'd also like to know if there are any other suggestions for Orchid bark, other than Orchiata, and advantages/disadvantages.