I'm with Cornflake on this--that's a tough topic to write about if you know nothing about it, particularly as a MC. i'm a psychologist and wouldn't know where to start. What kind of therapy? Evaluations? Consults? Occupational/industrial stuff? Forensics? There are a zillion kinds of therapy and different approaches for different issues. Most folks have good general knowledge, but also some specific populations/issues with which they are most comfortable. What's the story (what do you need)? This is the kind of thing that people who HAVE been in therapy (and there are so many, many who have) will immediately pick up on stuff that feels wrong. Are you envisioning a kind of Armistead Maupin-type collection of adorable therapy clients? Or...?
There are so many nuances to this that would be very hard to grasp if you have not had any experience and don't have access to an open and loquacious mental health provider. This came up in another forum where someone who obviously knew nothing about psychology or mental health decided it would be a neat plot point to have their MC (psychologist) reveal their own trauma history to a young client. We don't do that and it would be hard to make a credible story (unless the plot was about how a psychologist gradually decompensates, makes terrible decisions, eventually loses their license and so on.)
Of course, a lot of people get their information about psychologists from Hollywood, which is a terrible, terrible idea! While some of the movies are entertaining, we don't run off with our clients (Mrs. jones), or sleep with them/their families (Prince of Tides) or throw clients up against walls (Good Will Hunting) although all those thing are probably tempting at one time or another. As far as Hollywood goes, been a zillion years but I thought Judd Hirsh in Ordinary People did a really good job.
I don't know what drew you to this plot line, but I think you are going to have some serious research if you want to make this work, but I sure wish you the best with it!