Hello Jason! Good questions, as a member of class one I'd like to share my version of these question.
1. Your prospects could depend on what way you are planning on taking your training. I've seen our colleagues add on the training to their existing job or some of us have completely gone out on our own or a side job to start off. Being a body language trainer, one of the best ways to expose yourself and your skills is going out and interacting with your future clients, almost a no brainer. We are our own walking business cards. Me personally I've had to start attending networking events and got awkward with my new found skills. My recent target market has been entrepreneurs and those are plentiful. Eventually, you will meet people who fit your values as a trainer and make great connections. That then leads to word of mouth referrals, which can be given or asked for. All this aside from your normal marketing materials and social media presence.
2. My business has been a very steady growth in the last year, it has not ramped up aggressively, but using the techniques I described before I have been able to nurture some great connections and set myself up nicely. It's almost hard to actually cooperate in person with other trainer members since we are pretty spread out but we are good at keeping up with one or the other and sharing our success stories. A lot of us do work within the same niches: entrepreneurs, students, medical field etc. I've met 3 other people within my city who work with body language too but are outside of SoP, I've met with them as well no real sense of competition but great collaboration opportunities.
3. The best suggestion for clients is to do both, just like the trainer, it is good to practice what you preach. If a client is wanting to start off by learning about others without being aware of their own body language it almost feels inauthentic. The good thing about what we learn is the applications are very useful beyond a specification. If you teach a guy how to hold his body language during a first date he better present himself the same way in the second date. They will also be able to apply some of the knowledge in a work situation as well, outside of romance context. Us trainers usually over deliver on our trainings, the gift that keeps on giving. Also if it's not training others you can possibly be hired directly for certain jobs i.e. court hearings, interviews, observations etc.
I hope this helped some, cheers!