Shorter is better. Three to five minutes may best, but the content and your intended audience should determine the length of the program. Again, you don't have to tape everything. Good, short segments, even as short as 10 seconds, could be enough to get your point across. Good lighting is important.
Florescent lights can be fine.
Camera-mounted microphones are not the best way to pick up what people are saying. Consider buying a wireless or remote microphone. Instead, change camera positions while the camera is off to get different angles and perspectives. Have people talking as well as doing something. Get close-ups, because TV is an intimate medium.