I wish you the best of luck -- dogs with abuse/neglect histories can be even tougher to predict because so much more than breeding has shaped their behaviour before you even got there. You've taken on a big job in that little dog... the best dog training book I ever read was Brian Kilcommons' Good Owners, Great Dogs -- you should be able to take it out at the library if you don't want to buy it. It tackles easy and difficult subjects, and while I've had dogs whose behaviour in the end I've just had to live with (usually b/c I wasn't willing to put in what it would take to train something out), Kilcommons had good advice for every concern I've ever encountered over 20 years and three different dogs of widely varying receptiveness. Read as much as you can about breed type, too -- as I recall you have a brother who is a vet, and he should be able to tell you lots about Poms and their ways.
Because how we spend our days is, of course, how we spend our lives. -- Annie Dillard