Hi there, I don't have a lot of experience myself yet, but I will say that now I always repot immediately after buying, even if the plant is in bloom. I have found that it hasn't harmed the blooming of the plants much (except perhaps for a tiny miniature I just repotted), and you just can't know what's hiding if you don't get a good look.
The moss balls in the roots are really bad and all the roots right around there will be most likely dead, but so far the plants I got which had moss balls are doing ok (although one lost pretty much all it's roots, but seems to be slowly recovering!).
I don't use hydrogen peroxide myself.
I don't know the bark and peat mix you mentioned, but I have been warned against some mixes from garden centres as they can be old and have soured. I use bark bought online, or from orchid shows from the orchid growers themselves, however, of course if you want to repot asap then that isn't easy.
I use KLN, a liquid rooting hormone.
Good luck! Hope they all make it
