Would definately depend on your bioload and if you have live plants and such.
Some requirements will be higher than others depending on what fish you keep. For example: Discus and Rays require pristine water conditions. This usually results in large water changes every week. Goldfish are another due to waste they produce.
If you have just a couple fish in the tank such as neons, you could get away with about 10% every two weeks.
There's just too many variables involved. Unless you have an ideal setup like Bob where you don't run filters. ;o)
As for cleaning the media, just rinse it out in the old tank water when you do your changes. Replace it once it starts falling apart on you.
If cycled, weekly or every other week. And how much depends on your bioload. Water out in the wild contain 0 nitrates, so you want to keep your nitrates as low as possible. I would say below 20ppm if you have only fish. I keep mine under 10ppm due to sensitive inverts.
But since you have not cycled your tank yet.. if you keep fish you will need to do water changes every 2 days to keep ammonia and nitrites low.
Can't remember if you mention elsewhere, but do you have fish in your tank or are you cycling fishless? If fishless, no need for a water change until after you cycle.
If you have fish, you won't mess up the cycle by doing a water change. It continues no matter. Doing water changes in general make it go slower, but it is necessary if you have fish in the tank already to keep them alive. However, I would not do water changes until you detect ammonia in your tank. It took me nearly 4wks to register anything on my 75g tank.....but, I had a low number of fish (for my tank size) to start with and was doing water changes every 2-3 days.
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