What will you be streaming? To what platform? What's your target frame size or frame rate? What's the nature of the content-- high or low motion?
Is it a local application? How heavy is its CPU or GPU usage?
Best bet is to start with the Auto-Configuration Wizard in the Tools menu and then adjust as you have problems or complaints.
There are too many variables to give settings in response to specifications.
Bottom line is that if anyone asks if a MacBook Air is a good machine to stream on, the answer is, 'no'.