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To chip in as I used to have a 294MC Pro.
Gain 120 is where the high gain conversion mode kicks in and significantly reduces the read noise and offset 30 was what I used with mine.
And yes, bias frames are not useful with that camera, I would not bother shooting any. Apparently the built in circuitry on the chip times exposures under several seconds and over that (I don't know where the specific change over is) the ZWO designed external circuitry takes over. The best approach to flats is to use a dimmable flat panel and set up to use say 5 second exposures for flats, then you can shoot 5 second darks and create a master dark-flat to use with your 5 second flats. If you end up using a duo band filter you need to look at the histogram to see where the peaks are and adjust your target ADC upwards (And probably the panel brightness as well to keep to the same exposure time) as the average will probably be skewed downwards by the filter.
As for sensor temp I started with -15 and stuck with it as long as I had the camera, but dark current is still very low at -10 so I would probably go with that if I had one now as it makes the coolers job easier. Just like an aircon, the power required to cool is not linear per degree of cooling, -15 takes substantially more power than -10. Noise wise, even at -5 it is still less than 1 electron per pixel per minute so even a very long exposure for the camera (Say 10 minutes) is only going to add up to about 10 ADC across the image at 120 gain and a master dark should subtract it away nicely anyway.
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