I'm glad you are enjoying the book so far. And no, you are not being too forward in asking questions (and they are good questions, too.)
First, the issue of being on medication during pregnancy is a complicated one and depends a lot on the woman herself.
For women who are consciously committed to having their own children: for the sake of the baby's health some women make the decision to go off their medication during the pregnancy. The repercussions of this vary in severity from person to person, but it can be disastrous, enough so to keep one from doing it all in the first place. This is the "put my child first" approach which believes that the risk of possible disfigurement or retardation is enough to warrant the suffering of the mother during the risk of the term.
For women who are consciously committed to having their own children but who are not willing to go off their medication during a pregnancy: this could be for a number of reasons but may align itself with the "women's health" issue that sees that the potential risks of going off medication are severe enough to outweigh the risks involved in possible disfigurement to the child. The mother may make this decision not just for the sake of her own mental/emotional health, but for the effect it has on her husband, family, and society in general. If the risk of suicide or suicidal ideation is high when off meds, then the issue becomes one of a life-threatening nature.
But if I'm reading it right, your question was "if i was to get pregnant...would the Catholic Church allow us to plan on not having children?" Unfortunately your question lacks the consistency needed to answer it on one level alone. When you say "if i was to get pregnant," i assume that to mean you are asking hypothetically ask if you had already discovered you were pregnant. Your question then goes on to ask if the Church would "allow you to plan on not having children." To be consistent with the previous part of your question, this needs to be reduced to, "would the Church allow us to not have children?" The answer to this is unambiguous: since the child is in the womb already, any question of terminating the pregnancy is null and void, since the Church's stance on abortion is pretty clear.
If you were to assume, however, that you were not yet pregnant, but wanted to discuss whether or not the Church would allow you to PLAN on not having children, then that is a different question altogether, one which I can't speak with any steadfast assurance on. I do know that adoption is ALWAYS an option and encouraged in the Church...the decision to have children of one's own (i.e., biological) is a personal one, and one that some people will go to great lengths for--even going so far as to pay thousands of dollars for somebody else's egg or sperm just so they can experience the natural process of pregnancy and call the child "their own." I think parents of adopted children, however, do not consider their children any less their own than their biological children.
I will say that I am not in agreeance with the Church's teaching on the use of artificial contraception. I come at this from a theological perspective, but also from a personal one. I took NFP classes and it seems to work for some people...for others I think that the constant fear of pregnancy at a time when a couple is not financial or emotionally prepared for a child has the potential to do more harm to a marriage than the use of artificial contraception does. But that is a discussion for another time.
I would say that if you wanted to PLAN on "not having kids" with your husband, you would have to specificy if this meant not having biological children, or not being open to raising children at all. I think the Church would bless the former but not the latter if adoption was considered. But even this is open to debate, since recent developments in sacramental theology have acknowledged the bi-dimensional nature of marriage, which possessed both a "procreative" and a "unitive" function. The former was always given more weight, but both need to be considered equally.
2) The paper you are talking about is a voluntary committal waiver (in contrast to a "302" committal, which is non-voluntary). I did sign such papers when I was committed, but I would be willing to sign them over to my wife, on the condition that the criteria for such a committal are clearly defined beforehand to prevent the risk of being "whimsically" committed to an institution at the first sign of having a bad day.
3) I believe all things are possible in Christ. However, this decision again is an entirely personal one. For myself, I feel that in a marriage you are constant shifting weight from one partner to the other. I could fall in love with whoever I fall in love with, but marriage is always--and always has to be--a conscious choice. We make choices all the time. I choose not to be friends with people who are on drugs because I know that is not a good influence. I choose to invest in mutual funds rather than straight stock because I'm not comfortable with super high risk. You have to accept the consequences that come with all these choices. If I decide to marry someone who is fiscally irresponsible or who is a social butterfly, I know, to an extent, that this may pose some issues down the road. Since manic-depression is a lifetime condition, and marriage is a lifelong commitment, the decision to commit to someone with it is a heavy one and one that I personally do not feel comfortable in making. My own disease is sometimes all I can handle...to live a life with someone going through the same is one of those things that I think, for whatever reason, is not in either parties best interest. It's hard to bear someone else's burden of mental illness when you are having enough trouble bearing the burden of your own.
This, of course, is a conscious choice. But you might marry someone who gets diagnosed 10 years down the road, or gets cancer, or gets run over by a bus and is in a wheelchair. You can't anticipate that stuff and so you don't worry about it in the present because it doesn't yet--and may never--exist. THAT is when putting your trust and faith in God and his Providence really becomes a daily activity. Making choices with your God-given free-will--for better or for worse--places (paraphrasing Thomas Merton) "100% of the responsibility on you...and 100% of the responsibility on God").
Have to get to work now. Hope this was helpful. I love writing and answering questions, so don't hesitate to ask.