Every other day(especially in winter) could be too much - but it's impossible to say for certain, since contributing factors (temperature, humidity, media, size and composition of pot) to how quickly (or slowly) media dries vary so much.
Previously shriveled pbulbs aren't likely to replump, so don't judge by that. Pbulbs can also shrivel if the plant has been regularly over-watered; over-watering rots the roots, and the plant becomes unable to take up water, and so lives off the stored water in the pbulbs.
I also don't know for a fact that the rusty spots are caused by over-watering, but in the case where I had similar on a Mtssa, making sure it wasn't staying as wet DID seem to resolve the problem.
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