I wish I could offer some really great advice on how to parent a child like this effectively. I don't even know if there is a 'right' way to do it. Honestly, I winged it! She was my first, so I didn't know any better. It wasn't until she was over two that I realized not all toddlers were as crazy as her!
Things started to get easier for me when I stopped trying to be in control all the time. I picked my battles, lowered my standards and expectations (in terms of what I wanted to achieve on a daily basis) and, like I said before, held on for dear life. We have the most interesting plays put on in our house, too. There really is never a dull moment. It took me years to be able to relax and enjoy watching her be herself instead of trying to change it. I can only imagine how hard it is to juggle three kids who all have such differing needs! My hat is off to you. We planned to not have any more children based on DD. I know that sounds terrible, but it was so hard on our marriage. Luckily she conspired with Santa Claus and gave us an amazing present when her little brother came along when she was 6. I needed those 6 years to recooperate!
I can sympathize with your struggles with your own ADD as well. Going through testing with DD, I realized that I may also struggle with it. I had the same issues in school as you mentioned. My mom is convinced that I was (am) gifted as well, but I never had any formal testing. It gives you a much different perspective when you can empathize with your children's struggles. I think about what my brain is like and then I imagine her little brain battling being PG and ADHD. I can't even imagine how hard it was for her to deal with that before meds. No wonder she was so out of control.
I kept a diary when DD was little. I did not have any time to really write in it (HA!), but I would jot down funny things she did and said. I would often flip back through it and bust a gut at some of the stuff that happened in our house. At the end of a tought week I would read what happened and realized that I was justified at being tired. I have some pretty good material in that diary!
I read a lot of parenting books when DD was younger, but nothing seemed to apply to us or work. I just followed her cues and kept being consistent with my behaviour expectations. She was a smart kid and she figured it out. We avoided situations that we knew she could not be successful in (sit-down restaurants and movies) and we modified things so that WE felt like we were doing a good job. In reality, we were just heading off disaster. But, if worked for us in the short term and it helped us cope.
Again, big hugs to you. Your kids are lucky to have a mommy who cares enough to WANT to learn how to be a better parent.