Welcome on board. It does get a lot faster for you when the site gets to know you. There is a lot of help here. What I found even more - a sense of empowerment here. I really needed that.
Read that book - I had been a member of this site for several years before I actually got my hands on the book (I borrowed it form the library). I was impressed with it from the beginning and was wading through the book, waiting to get to the "this is how you do it" section. But even before I got that far, I noticed difficult child 3's behaviour improving. Of course, it wasn't because I had already begun doing everything right; it was because I had made some changes already to my own behaviour, without realising. And those changes were snowballing positively and I loved the improvement. Not a cure; we still have the underlying disorders to deal with, but it makes it a lot easier to cope with what is left.
What I needed to do most, was change my own approach to my child. All the usual "good parenting" I had had prided myself on, was actually making him worse. I call it a change of mindset that is needed, in order to help your child more effectively.
Discipline is important, especially with a problem child. But sometimes when we respond to bad behaviour by clamping down even more firmly, we make the problems worse. Instead, try to find a way to focus the child's stubbornness into self-discipline. A child who can so effectively be oppositional is also a child with a great capacity for self-discipline. And once they are given the reins, you can still steer a little but let them feel they are the ones in control. You can often find these kids taking surprisingly moral paths in life, all you have to do is provide guidance and the map. You become the child's facilitator and helper, rather than the person with the whip and chair.
Anyway, read around on this site, you will find a lot of other people with similar problems. You are not alone!
Marg