I have adopted 4 OTTBs. 1 was a bit nuts, but I knew that before I got him! 2 are really laid back and kind and very easy to work with. 1 is amazing, but a little insecure so he needs a confident rider and then he's fine. When you shop, as with any kind of horse, take an experienced horse-person with you to assess their personality, soundness, movement, training, etc.
I would suggest you find a trainer other than Clinton Anderson to emulate, though. Each trainer develops their techniques around a specific type of horse. He works primarily with western types. OTTBs are very sensitive, athletic, energetic and hard-working. They do require a specific type of handling to do well. Their are books, websites, and blogs about training OTTBs. Check them out!