I'm scared of parenting my children since I'm Bipolar II?

I am a 27 year old woman who has had Bipolar II all my life. I take medications and am VERY self aware of when I'm about to have an episode. I have a 3 year old son and two stepsons, one 6 and one 3. We are trying to get custody of my husband's sons and one of them has Oppositonal Defiant Disorder. My son has a genetic disorder and before the age of 1 I had to watch him go through chemotherapy, a blood cord transplant, and almost die. He is fine now except for some mild hearing loss. Up until this point I have been able to be a very good mother to my son. I did have a nervous breakdown, but was smart enough to know that I had to be hospitalized and I checked myself into an institution so that I could get better. I have always put my son first and that means taking good care of myself and my mental health so that I can take care of him. I am just worried that bringing in a child who has a disorder will make it harder on me and I won't be as efficient of a mother for all three of them. I love all three of these boys and I want to be the best mother and step-mother to them that I can be, but I am terrified that dealing with someone else who has a disorder will trigger mine. I am doing lots of research on his illness and am currently reading a book and taking detailed notes of the symptoms and how to help him. I guess what my question is, is since I have a disorder, does that make me at risk for being a bad parent? There is nothing more in the world that I want to be than a mother, I love these boys and I want them to be in a home and have lives that are as happy and as stable as is possible. I am just scared. Is this normal to be scared? I've tried looking at websites but all they tell me is to take my medicine and keep track of my moods, things I already do. Is there anything more I can do. I know that these are a lot of questions but if someone out there has this same disease please help me or give me some comfort. Thank you.