How abundant are positions for teaching ESL to business people?

Fairly common. The cool thing about this program too is that it'll put you in touch with some private language institutes in NYC / Boston / wherever you're studying. I'd recommend choosing a class in the city where you'd like to teach if you can.

You'll also be teaching adults in your practice sessions (18+) which is a good intro to teaching business people later on.

There are so many positions out there to teach English to businesses/ business professionals. I have taught several classes myself- in fact they were always the best classes to teach! One thing to keep in mind is that most companies will hire an ESL teacher for their employees through a language school. The reason for this is that companies want to make sure they are getting the best quality of teacher(s) they can. So if you do not have one already, look into getting a CELTA!