I just got this camera also, and I'm interested in the answer too. But I don't see the need to think too much about gain settings. At gain 0 you have the highest DR, full well and only a little over 3e read noise. That's great for LRGB. Then gain 100 is the magic number where you don't lose much DR but the read noise drops dramatically to around 1.3e. The only negative is that the full well does drop some at gain 100, but this is irrelevant for narrowband. So I plan to use gain 0 for LRGB and gain 100 for narrowband. In fact, the ASCOM driver doesn't even go over 100, probably because there isn't anything to "gain" going over 100.
Offset isn't super critical so I just stuck with 50 which is what ZWO has as the default.