Something that will get you at least 90% (and maybe everything) you want would be to get a Magic 260 controller and then control it with a a Behringer FBC1010.
With this rig you can use the FBC1010 to select up to 100 "Shows." A "Show" is either a static light setting, or lighting setting in which the lights are changing over time, either with the beat via tap tempo or audio or with set changes at set times.
You would be able to cause a dim by selecting selecting a dim Show(eithet a black out or to a preset low light level) and set the fade time to whatever you want.
There may be a way to control the overall light intensity (master fader) with the FCB1010 pedals, but if there is, I'm not aware of it. you may have to compromise by setting the overall (master fader) by hand on the face of the M260.
The manual neither unit is all that clear as to how to do this. I would be able to walk you through it.