This is an opinion of an ex-MSF instructor with thousands of graduates. Just my opinion.

In the class you will be riding 250cc bikes. Light weight, light steering. Given your size, the Bonneville would be a good first bike. It feels light and has lighter steering that the America or Speedmaster. In other words, your training will translate well to the Bonnie.

IMHO, a 250cc bike is too small for you on the open road. The Bonnie would be a good balance and you'll enjoy several years of ongoing training (aka road riding). When you feel comfortable, you can then move up if you so desire.