Ralph - I agree with most of what you said. The downside of many "professional models" is that if you book them through an agency, they're usually one of two types - runway models who think in terms of fashion poses only, or "boudoir" models with surgically enhanced body parts who only know how to do erotic modelling. This is not to say you can't find someone who will fit what you are looking to do through an agency, but it is less likely. I would definitely give the local universities and art schools a try.