to summarise muslims are encouraged to have children, men are told to marry fertile women, and unless there is a reason to stop having children (like its harmful for mother/kids had to be delivered by c-section etc) then it is not allowed.
contraception is allowed but not on a permanent basis
umar radhiallahu anhu use to force himself to cohabit (i cudnt find a better word :hidingwith his wives at times when he felt no desire whilst making the dua' " oh Allah bestow upon me a son who will glorify you"
SOURCE: Seerah of Umar - Anwar Al-Awlaki
Explenation: Allah grants lives, and Allah takes care of them for those who have Tawwaqul, it might seem like your not financially fit etc to take care of so many but then who knows where Allah will give rizq from.
I don't think that what you're thinking is necessarily haraam, but you have to be careful because certain contraceptives, particularly birth control pills which have an effect on your body are haraam. And, Allah will decide what is best for you and your family.