The approach depends on the audience's knowledge level of the topic, prevailing attitudes and the goals of the organization sponsoring the program. If the audience anticipates certainty or your goal is to motivate them, evaluate the panel format carefully. A single powerful speaker is more likely to get buy-in to the topic. Alternatively, structure the panel to reaffirm the proposed solution. But if your topic is how to lose weight and four panelists each promote a different diet, the audience is likely to be confused and do nothing.
Panels work well with in-house presentations, allowing different sectors of the enterprise a voice.
Panelists do not need to rehearse but do need to have interacted on some level in advance. The moderator introduces the topic, the format and the panelists. The audience will want to know why you have chosen the approach. Omit the part about her pet rhino and ten kids. Indicate how individual speakers will be introduced.